Chapter 8: Code 39's Limitations |
Executive Summary |
Code 39, invented in 1974, was a revolutionary symbology as the first barcode capable of encoding both numbers and letters. However, its very design---encoding each character with nine elements where three are wide---makes it inherently inefficient with space. This chapter examines how Code 39's technical characteristics, particularly its low information density and mandatory quiet zone requirements, have created practical challenges across multiple industries. While Code 39 remains in use today due to its widespread compatibility and self-checking properties, its limitations have driven many sectors toward more efficient symbologies like Code 128 and 2D codes. We will explore real-world examples from healthcare, defense, automotive manufacturing, logistics, and government sectors to illustrate how these technical constraints manifest in operational practice. |
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1. Introduction: The Revolutionary That Became a Bottleneck |
To understand Code 39's limitations, we must first appreciate what it achieved. Before Code 39, barcodes were largely confined to numeric data. The Universal Product Code (UPC) could only encode digits, which was sufficient for retail point-of-sale applications but entirely inadequate for industries that needed to track items using alphanumeric identifiers---serial numbers, part codes, or asset tags that naturally contain letters. |
Code 39, developed by Intermec in 1974 and also known as Code 3 of 9, USD-3, or LOGMARS, broke this barrier . It could encode uppercase letters A through Z, digits 0 through 9, and a handful of special characters including space, dollar sign, period, minus, plus, slash, and percent---43 characters in total . This made it the first practical symbology for applications beyond retail shelves. |
The U.S. Department of Defense recognized this potential and adopted Code 39 as the standard for labeling military equipment under the LOGMARS (Logistics Applications of Automated Marking and Reading Symbols) program . This endorsement gave Code 39 immense credibility and drove its adoption across government and defense contracting. Soon, it became the de facto standard for asset tracking in manufacturing, healthcare, and logistics. |
However, the very architecture that made Code 39 alphanumeric also imposed severe limitations. Each character in Code 39 consists of five bars and four spaces---nine elements in total---with exactly three of these elements being wide . This 'three of nine' structure means that every character consumes a significant amount of horizontal space. When data needs grew beyond short identifiers, Code 39's low density became a major operational problem. |
Today, Code 39 is described as having a practical capacity of 20 to 30 characters, with a maximum of about 50 characters . In comparison, Code 128 can pack roughly twice as much data into the same physical space. This difference is not merely academic---it translates directly into label size constraints, scanning reliability issues, and operational friction in real-world applications. |
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2. Technical Foundations: Why Code 39 Is So Wide |
To appreciate why Code 39 presents challenges in practice, we need to understand its encoding mechanism in some detail. The technical term 'width-encoded' describes Code 39's fundamental approach: information is represented not just by the presence or absence of bars, but by the relative width of those bars and spaces. |
2.1 The Three-of-Nine Structure |
Code 39 gets its name from its encoding structure: each character is represented by a pattern of nine elements---five bars (dark lines) and four spaces (light gaps between bars) . Within these nine elements, exactly three are wide and six are narrow . The wide elements carry the information; the narrow elements serve as the baseline. |
The ratio between wide and narrow elements can range from 1.8:1 to 3.4:1, with 2:1 being the most common . This means a wide bar might be twice as thick as a narrow bar. The specific pattern of which three of the nine positions are wide determines which character is encoded. For example, an 'A' has a different wide-element pattern than a 'B' or a '1.' |
This encoding approach is elegant but costly in space terms. Because three out of every nine elements must be wide, a Code 39 barcode cannot be compressed beyond a certain point. Every character, regardless of what it represents, consumes the same number of element positions. |
2.2 The Intercharacter Gap |
Code 39 is a 'discrete' symbology, meaning each character is separated from the next by a distinct gap. This intercharacter space is always narrow (one module wide) and is not part of any character's encoding---it simply serves to separate characters . While this makes Code 39 easier to decode (the scanner can easily identify where one character ends and the next begins), it adds to the overall length. In contrast, 'continuous' symbologies like Code 128 use spaces that are part of the data encoding, achieving greater density. |
2.3 Start and Stop Characters |
Every Code 39 symbol begins and ends with an asterisk (*) character, which serves as a start/stop marker . This character is encoded using the same three-wide pattern as any other character. The asterisk tells the scanner where the barcode begins and ends. While this provides reliable framing, it adds two additional characters of width to every symbol---overhead that becomes significant when encoding short data strings. |
2.4 The Extended Code 39 Variant |
A variant called Code 39 Extended (or Code 39 Full ASCII) was later developed to encode the full 128-character ASCII set, including lowercase letters and additional symbols . However, this extension came at a steep cost: each lowercase letter or extended character requires a combination of two Code 39 characters to represent a single data character . For instance, a lowercase 'a' is encoded as the pair '+A'. This effectively doubles the length of barcodes containing lowercase letters or special characters, compounding the density problem . |
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3. The Quiet Zone: A Critical but Costly Requirement |
Code 39 requires a 'quiet zone' or blank margin on both the left and right sides of the barcode. This is not merely a suggestion---it is a mandatory part of the symbol specification. |
3.1 What Is a Quiet Zone |
The quiet zone is an empty area of blank space that precedes the start character and follows the stop character . It must be completely free of any marks, text, graphics, or decorative elements. Its purpose is functional, not aesthetic: the scanner uses the transition from this blank space to the first bar to calibrate its optical sensors and determine where the barcode begins . |
Think of the quiet zone as punctuation. Without it, the scanner cannot distinguish between the barcode and its surrounding environment. If text or graphics encroach into this space, the scanner may interpret those visual elements as part of the barcode data, leading to misreads or complete failure to decode . |
3.2 The 10X Requirement |
For Code 39, the quiet zone must be at least 10 times the width of the narrowest element (called the X dimension) on each side . This means if the narrowest bar is 0.010 inches wide, each quiet zone must be at least 0.100 inches---a fifth of an inch total for both sides, before any data characters are even printed. |
In practice, this quiet zone requirement is a significant factor in Code 39's overall size. A barcode that is already wide due to its encoding structure must be made even wider by the mandatory blank space surrounding it. For small labels or products with limited packaging space, these margins can be the difference between a barcode that fits and one that does not. |
3.3 Real-World Impact of Quiet Zone Requirements |
In packaging design, the quiet zone is often overlooked, and violations are reportedly the single most common cause of barcode scanning failures . Graphic designers may place text, logos, or decorative borders too close to the barcode. Package seams, folds, or curved edges may intrude into the margin. When the barcode is printed on corrugated cardboard or curved surfaces, the effective quiet zone may be reduced even if the label design meets specifications on paper . |
In a high-speed logistics environment, a barcode with insufficient quiet zone might scan occasionally in ideal conditions but fail when the package is tilted, moving quickly, or illuminated differently. This intermittent failure is particularly problematic because it may not be caught during initial testing but will cause operational slowdowns in production. |
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4. Industry Application Case Studies |
The technical limitations of Code 39 manifest differently across industries. The following case studies illustrate how Code 39's characteristics---its low density, quiet zone requirements, limited character set, and extended-mode overhead---interact with specific operational needs. |
4.1 Healthcare: Patient Identification and Specimen Tracking |
The healthcare industry was an early adopter of Code 39, particularly for patient identification wristbands and laboratory specimen labeling. The Health Industry Bar Code (HIBC) standard originally specified Code 39 for many applications. |
The Application: A hospital patient wristband contains the patient's medical record number, date of birth, and other identifiers. Laboratory specimens require labels that link the sample to the patient and include information about the test being performed. |
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How Code 39's Limitations Affect Healthcare: |
The first practical issue is wristband space. Patient wristbands in hospitals are typically narrow---often less than an inch in height. Code 39's density requires the barcode to be either very long horizontally (which may not fit on a wristband that wraps around a patient's arm) or printed at such a small scale that reliability suffers. |
The quiet zone requirement compounds this problem. On a narrow wristband, designers may be tempted to reduce the quiet zone to save space, only to discover that the barcode no longer scans reliably at the bedside, particularly in dim lighting or when the wristband is curved around the patient's arm. |
The character limitation is also significant. Patient identifiers often include letters, numbers, and sometimes hyphens. Code 39's base character set can handle this. However, if the identifier includes lowercase letters (as many electronic health record systems generate), the hospital must either encode the data in uppercase only or use Code 39 Extended, which doubles the barcode length . For a patient with a long medical record number, the resulting barcode may simply not fit on the wristband. |
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Operational Consequences: |
When a wristband barcode fails to scan at the bedside, nurses must fall back to manual data entry. This is not merely an inconvenience---it is a patient safety risk. Manual entry introduces the possibility of errors, and the time spent typing long alphanumeric strings takes staff away from direct patient care. Hospitals that have transitioned from Code 39 to more compact symbologies like Code 128 or Data Matrix on wristbands report significant improvements in scanning reliability and workflow efficiency. |
A Practical Workaround: |
Some healthcare facilities continue to use Code 39 for wristbands but limit the amount of data encoded, storing the full patient record in a database and using the barcode only as a key. This works as long as the identifier is short enough to fit comfortably on the wristband with adequate quiet zone. When identifiers grow beyond the 20-character practical limit, however, this strategy fails. |
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4.2 Department of Defense and LOGMARS |
The U.S. Department of Defense's LOGMARS program was arguably the most significant driver of Code 39 adoption. MIL-STD-1189B formally specified Code 39 for military equipment labeling . |
The Application: Military equipment---from small components to entire vehicles---must be labeled with unique identifiers for tracking throughout the logistics chain. These identifiers often include alphanumeric strings that denote the item's national stock number, serial number, and other classification data. |
How Code 39's Limitations Affect Defense Logistics: |
The military's identification systems have evolved, and the data strings they require have grown longer. A modern item unique identification (IUID) marker may need to encode a Global Individual Asset Identifier (GIAI) or other long alphanumeric sequence. Code 39, with its limited practical capacity of 20-30 characters, cannot comfortably encode these longer identifiers . |
The quiet zone requirement is also problematic for military equipment. Items may be irregularly shaped, and labels may be applied in locations where blank space is at a premium. On a small component or a curved surface like a rifle stock or a vehicle part, providing the necessary 10X margin on each side can be challenging. |
The Shift Away from Code 39: |
The Department of Defense has recognized these limitations and has increasingly moved toward 2D symbologies like Data Matrix, which can encode far more data in a fraction of the space and require only a one-module quiet zone . However, legacy systems and long-standing contracts mean that Code 39 remains in use for many existing applications. The transition has been slow, with many contractors required to support both the new Data Matrix labels and the older Code 39 markings for compatibility with fielded equipment and reading infrastructure. |
A Real-World Incident: |
While specific military incidents are rarely publicized, logistics personnel have described situations where Code 39 labels on equipment pallets failed to scan because the quiet zone was insufficient---often because another label had been placed too close, or because the label had been applied on a curved surface that effectively reduced the readable margin. In a military supply chain where time pressure is extreme and equipment must move rapidly, these scanning failures cause delays that have real operational impacts. |
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4.3 Automotive Manufacturing |
The automotive industry has long used Code 39 for parts tracking and assembly line management. Vehicles are assembled from thousands of components, each requiring accurate tracking from supplier to assembly line. |
The Application: Automotive suppliers label parts with barcodes that identify the part number, supplier, batch, and other traceability data. These labels must survive harsh environments---oil, grease, heat, and physical abrasion---while remaining scannable throughout the manufacturing process. |
How Code 39's Limitations Affect Automotive: |
Modern automotive manufacturing relies on just-in-time (JIT) logistics, where parts arrive at the assembly line exactly when needed. In this high-pressure environment, scanning failures are costly: if a barcode on a parts bin fails to scan, the line may stop while a worker manually identifies the parts or retrieves the correct label. |
The density limitation of Code 39 means that parts labels with detailed traceability data can become quite long. On a small component, there may simply not be enough surface area to print a Code 39 label that includes all the required data and the mandatory quiet zones. Suppliers have been forced to either use larger labels (which may not fit) or reduce the amount of data encoded (which compromises traceability). |
The Problem of Print Quality: |
Code 39 is a width-encoded symbology, meaning it relies on accurate differentiation between wide and narrow elements. In the harsh environment of an automotive factory---where labels may be printed on thermal transfer printers that are subject to dust, heat, and wear---maintaining the required wide-narrow ratio can be challenging . Slight ink spread during printing or wear on the print head can make wide and narrow bars indistinguishable, causing scanning failures. |
Industry Response: |
Many automotive manufacturers have transitioned to Code 128 or 2D symbologies for parts labeling. These symbologies are more robust in challenging printing environments and offer higher density. However, as in defense, the installed base of Code 39-compatible scanners and legacy systems means the transition has been gradual. Suppliers often find themselves maintaining two labeling systems or printing labels that include both Code 39 and a more modern symbology to support both current and legacy readers. |
A Concrete Example: |
Consider a tier-one automotive supplier providing brake calipers to an assembly plant. The label on each caliper must include the part number (10 characters), supplier code (5 characters), date of manufacture (8 characters in YYYYMMDD format), and batch number (6 characters). This is 29 characters of data. Even at the minimum practical bar width, a Code 39 label encoding this data may be four to five inches long. On a brake caliper---an irregularly shaped metal component---finding a flat area large enough for this label, plus the 10X quiet zones, is difficult. The supplier may be forced to wrap the label around a curved surface, further degrading scan reliability. |
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4.4 Warehousing and Logistics |
The logistics industry was an early Code 39 adopter, using it for pallet labels, storage location tags, and shipping documentation. |
The Application: Warehouse management systems use barcodes to track inventory movements. Items are scanned when received, moved to storage locations, picked for orders, and shipped. Each scan must be fast and reliable. |
How Code 39's Limitations Affect Logistics: |
In a modern warehouse with high ceilings and long aisles, workers often scan barcodes from a distance. Code 39's density means that a long barcode may be too wide to be easily captured by handheld scanners, particularly if the label is on a high shelf and the worker is scanning from floor level. |
The quiet zone requirement is also problematic in the warehouse environment. Labels on pallets or storage bins can become partially covered by adjacent items, tape, or debris. If even a small portion of the quiet zone is obscured, the scanner may fail to read the entire symbol . In contrast, 2D symbologies with their smaller quiet zone requirements and built-in error correction are more robust to such partial obscuration. |
The Challenge of Long Identifiers: |
Modern supply chain tracking requires longer and longer identifiers. GS1 standards for logistics labels, such as the SSCC (Serial Shipping Container Code), are 18-digit numbers. When combined with application identifiers and other data, a logistics label may need to encode 30 or more characters. In Code 39, this results in a physically large label that may not fit on a standard 4x6-inch shipping label if the required quiet zones are also included. |
Operational Friction: |
Warehouse managers who have transitioned to Code 128 or 2D codes report significant improvements in first-pass read rates---the percentage of barcodes that scan correctly on the first attempt. First-pass read rates below 95% are considered problematic in high-volume logistics; with Code 39, achieving high first-pass rates on long barcodes can be difficult, particularly in challenging warehouse conditions. |
A Realistic Scenario: |
A large e-commerce fulfillment center receives a pallet of merchandise from a supplier. The pallet label is a Code 39 symbol encoding a 25-character supplier purchase order number. The label is printed on a 4x6-inch thermal label and applied to the side of the pallet. When the pallet arrives at the receiving dock, the worker scans the label with a handheld scanner. If the label is slightly wrinkled (common on pallets that have been shrink-wrapped), or if the scanner is held at the wrong angle, the barcode may fail. The worker must then reposition the pallet or manually enter the purchase order number---a delay that, in a facility processing thousands of pallets per day, adds up to significant lost productivity. |
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4.5 Manufacturing and Asset Tracking |
Beyond automotive, Code 39 has been widely used in general manufacturing for tracking work-in-progress, finished goods, and capital equipment. |
The Application: In a factory, barcodes are applied to raw materials, subassemblies, and finished products to track their movement through the production process. Capital equipment (machine tools, test equipment, forklifts) is tagged for maintenance and inventory tracking. |
How Code 39's Limitations Affect Manufacturing: |
One of the most significant challenges in manufacturing is the variety of surfaces on which barcodes must be printed. Labels may be applied to metal parts, plastic housings, cardboard boxes, or directly to components using direct part marking (DPM). Code 39, like all 1D barcodes, is susceptible to print quality issues on rough or reflective surfaces. |
The density limitation also matters in manufacturing. A work-in-progress label might need to encode a part number, a manufacturing order number, a serial number, and a quality status code. Depending on the specific identifiers used, this data string can easily exceed 30 characters, pushing Code 39 to its practical limit . |
The Economic Impact of Scanning Failures: |
In a factory, the cost of a scanning failure is not merely the time it takes to manually enter the data. A failed scan on a production line can mean that a subassembly is not properly recorded as having completed a process step, potentially causing production scheduling errors downstream. In regulated industries (aerospace, medical devices, automotive), accurate traceability is a regulatory requirement; incomplete tracking can lead to product recalls or regulatory sanctions. |
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4.6 Government and Public Sector |
Beyond the Department of Defense, many government agencies have used Code 39 for asset tracking, document management, and identification cards. |
The Application: Government agencies manage inventories of equipment (computers, furniture, vehicles), track documents in filing systems, and issue identification badges to employees and contractors. |
How Code 39's Limitations Affect Government: |
Government asset tracking often involves very long identifiers---equipment serial numbers, contract numbers, or budget codes can be quite lengthy. Code 39's limited practical capacity makes encoding these complete identifiers difficult; agencies often compromise by encoding only a shortened identifier and relying on a database to store the full details. This approach works but introduces complexity: if the database is unavailable or if the shortened identifier is not unique, the system fails. |
The quiet zone requirement is also problematic for identification badges. Badges are typically credit-card sized, and space is at a premium---there must be room for the photo, agency logo, employee name, and the barcode. A Code 39 barcode on a badge with sufficient quiet zone may be quite narrow, potentially reducing scan reliability. |
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4.7 Airline and Aviation |
The airline industry has used Code 39 for tracking aircraft parts (as mandated by some aviation regulatory frameworks) and for boarding passes in some older systems. |
The Application: Aircraft maintenance requires meticulous tracking of every part used on an aircraft. Parts must be traceable to their manufacturer, batch, date of manufacture, and installation history. Boarding passes need to encode passenger information and flight details. |
How Code 39's Limitations Affect Aviation: |
Aircraft parts labels are typically small and must fit in confined spaces on aircraft structures and components. Code 39's density is a significant limitation: a part number with a long serial number may produce a label that is too wide for the available space. Additionally, the quiet zone requirement may be impossible to meet on irregularly shaped aircraft parts that lack flat surfaces with adequate margins. |
For boarding passes, the passenger name, flight number, date, seat assignment, and frequent flyer number can easily exceed 30 characters. Code 39 would produce a very long barcode that may not fit on a standard boarding pass. As a result, most airlines have transitioned to Code 128 or PDF417 (a 2D symbology) for boarding passes, with Code 39 largely relegated to legacy systems. |
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4.8 Inventory and Retail Support |
While Code 39 is not typically used for retail point-of-sale (that role belongs to UPC and EAN), it has been widely used for internal retail operations: shelf labels, backroom inventory tracking, and vendor shipments. |
The Application: Retailers track inventory in the backroom using barcodes on shelf tags and storage bins. Vendors label shipments with barcodes that encode purchase order numbers and other transaction data. |
How Code 39's Limitations Affect Retail: |
The challenges here are similar to those in warehousing. Shelf labels in retail environments often include product information (short descriptions, price, stock-keeping unit) that can be lengthy. The available space on a shelf edge is limited, and the quiet zone requirement means that a Code 39 label may be too wide to fit on a narrow shelf tag. |
Additionally, retail inventory audits require rapid scanning of many items. If Code 39 labels fail to scan at a high rate (due to print quality issues, quiet zone violations, or physical damage), the audit is slowed, and data quality is compromised. |
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5. The Extended Code 39: A Solution That Created a New Problem |
The Code 39 Extended symbology was developed to address the limited character set of standard Code 39, specifically the inability to encode lowercase letters and the full ASCII symbol set . The approach was conceptually simple: use two-character combinations to represent each extended character. For example, lowercase 'a' is encoded as the pair '+A' . |
The Technical Approach: |
The extended mode works by defining a set of 'shift' characters that modify the meaning of the following character. A scanner configured to recognize Code 39 Extended interprets these two-character combinations as a single data character. The encoding is standardized, so any Extended-compatible scanner will decode them correctly. |
The Cost: |
The cost of this extension is substantial: every lowercase letter or extended ASCII character doubles the number of Code 39 characters required to encode it. A data string of 10 lowercase letters would require 20 Code 39 characters to encode, plus the start and stop asterisks. The resulting barcode is roughly twice as long as it would be if lowercase letters were natively supported . |
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Practical Implications: |
In applications where lowercase letters are necessary---for example, encoding an email address or a case-sensitive identifier---Code 39 Extended produces barcodes that are often impractically long. The quiet zone requirement, which is specified as a multiple of the narrow element width, means that longer barcodes require even wider margins. |
For instance, consider encoding the identifier 'aBc123-XyZ' (10 characters, including lowercase and uppercase letters, digits, and a hyphen). In standard Code 39 (assuming uppercase only), this could be encoded as 'ABC123-XYZ' (same number of characters if we upcase the letters). But if case sensitivity is essential, Code 39 Extended would encode lowercase 'a' as two characters, lowercase 'c' as two characters, lowercase 'y' as two characters, and the hyphen as one character (since hyphen is in the standard set). The total character count in the barcode would be the start asterisk, plus 4 characters for the two lowercase letters (2 each), plus 6 characters for the uppercase letters and digits (1 each), plus 1 for the hyphen, plus the stop asterisk---approximately 13 characters total, compared to 10 characters if case sensitivity were not required. |
But if the entire string were lowercase letters, the expansion would be more dramatic. A string of 20 lowercase letters would require 40 Code 39 characters to encode, resulting in a barcode approximately 4 inches long at typical print densities, plus the quiet zones on both sides. |
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Scanner Compatibility Issues: |
Not all barcode readers support Code 39 Extended by default . Scanners often require configuration or programming to recognize the two-character combinations and decode them as single characters. In a mixed environment where some scanners are configured for Extended mode and others are not, the same barcode may decode differently---an Extended-aware scanner might decode '+A' as lowercase 'a', while a standard scanner would decode it as the character pair '+A'. This compatibility issue is a significant barrier to deploying Code 39 Extended in many operational settings. |
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6. Comparison with More Efficient Symbologies |
To fully appreciate Code 39's limitations, it is helpful to compare it with the alternatives that have largely replaced it. |
6.1 Code 128 |
Code 128, developed in 1981, was designed specifically to address Code 39's density problem. It is a continuous symbology (no intercharacter gaps) that encodes each character in fewer elements than Code 39. The result is that Code 128 is approximately 30% denser than Code 39---meaning a Code 128 barcode encoding the same data is about 30% shorter . |
Code 128 also supports the full 128-character ASCII set natively, without requiring the two-character expansion that Code 39 Extended uses. This means lowercase letters and special symbols do not increase the barcode length. |
Code 128 has largely replaced Code 39 in logistics, healthcare, and automotive applications where space is at a premium. Its adoption has been driven by the same forces that created pressure for a more efficient symbology---longer data strings, smaller labeling surfaces, and the need for higher first-pass read rates. |
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6.2 Data Matrix and QR Code (2D Symbologies) |
2D symbologies offer even greater density than Code 128. A Data Matrix or QR Code can encode hundreds of characters in a square symbol that might be less than half an inch across. |
For applications requiring quiet zones, 2D symbologies are also more forgiving. Data Matrix requires only a single module of quiet zone on each side---far less than Code 39's 10X requirement . This makes 2D codes particularly suitable for small items, direct part marking, and applications where label space is extremely constrained. |
In healthcare, many hospitals have transitioned from Code 39 wristbands to Data Matrix or QR Code wristbands, allowing them to encode full patient identifiers (including letters, numbers, and symbols) in a compact square that requires minimal margin. |
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6.3 Code 93 |
Code 93 was developed as an improvement on Code 39. It offers higher density and includes a built-in check digit for error detection. However, Code 93 never achieved the same level of industry adoption as Code 39 or Code 128, partly because it was introduced between the two more successful symbologies and partly because its licensing terms were initially more restrictive. |
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7. When Code 39 Makes Sense Today |
Despite its limitations, Code 39 remains in use and is often the right choice in certain scenarios. |
Legacy Systems: Many organizations have extensive investments in Code 39-compatible scanners, printers, and software. Replacing these systems is expensive and time-consuming. For these organizations, continuing to use Code 39 for applications that do not require long data strings is the most cost-effective approach. |
Simple Applications: For encoding short identifiers of 10-15 characters, Code 39 is perfectly adequate. The barcode will not be excessively long, and the quiet zone requirement is manageable. For simple asset tags, internal inventory tracking, and similar applications, Code 39 works fine. |
Uncertified Printing Environments: Code 39's self-checking property---where a single print defect is unlikely to create a valid character---makes it more forgiving of print quality variations than some other symbologies . In environments where print quality cannot be tightly controlled, Code 39 may be more reliable than Code 128. |
Low-Volume Operations: For a small business or a non-profit organization with low scanning volumes and basic labeling needs, Code 39 is simple to implement, widely supported, and inexpensive. The costs of Code 39's limitations are only significant when scanning volumes are high or when label space is extremely constrained. |
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8. Workarounds and Mitigation Strategies |
Organizations that need to continue using Code 39 despite its limitations have developed several workarounds. |
Reducing the Data Encoded: Rather than encoding a full identifier, some organizations encode a short 'key' and use a database to look up the associated data. For example, rather than encoding a full 25-character part description, the barcode might encode a 10-character part number that the system uses to retrieve all other details. |
Using the Largest Practical Label: Where label space permits, using a larger label with a larger X dimension can make Code 39 more reliable. A larger quiet zone (beyond the required 10X) also improves scan reliability . |
Careful Label Design: Following quiet zone best practices---clearly marking the quiet zone as a no-print area in label design files, verifying that text and graphics do not encroach, and using label verification equipment to measure quiet zone compliance---can prevent many Code 39 scanning failures . |
Printing Quality Control: Using high-quality thermal transfer printers, maintaining print heads, and using properly rated labels can reduce the print quality issues that cause Code 39 scanning failures. |
Using Code 39 Extended with Caution: When lowercase letters are absolutely necessary, Code 39 Extended can be used, but organizations should be aware of the doubling effect on barcode length and should ensure that all scanners in their environment are configured to support the Extended mode . |
Dual Encoding: Some organizations print both a Code 39 barcode and a 2D code on the same label. The Code 39 barcode supports legacy scanning systems, while the 2D code provides the density and error correction needed for modern scanning. |
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9. Summary and Conclusion |
Code 39 stands as a pivotal milestone in barcode history---the first alphanumeric symbology, the enabler of logistics tracking, and the standard that brought barcodes beyond retail. Its self-checking property and widespread compatibility have kept it in active use for half a century. |
Yet the very design that made Code 39 revolutionary has become its principal limitation. The three-of-nine encoding structure that gives it its name requires every character to occupy nine element positions, three of which must be wide. This width-encoded architecture, combined with mandatory intercharacter gaps and a 10X quiet zone on each side, makes Code 39 approximately 30% less dense than Code 128 and dramatically less efficient than modern 2D symbologies. |
Across industries, these technical constraints have manifested as practical problems. In healthcare, Code 39 wristbands struggle to encode long patient identifiers while maintaining reliable scanning at the bedside. In defense logistics, legacy LOGMARS labels cannot accommodate modern item unique identification requirements. In automotive manufacturing, Code 39 parts labels are limited by label space on small components and challenged by harsh printing environments. In warehousing, the quiet zone requirement makes labels vulnerable to partial obscuration. In government, asset tracking with Code 39 often requires truncating identifiers or relying on database lookups. |
The Extended variant of Code 39 attempts to address the limited character set by encoding lowercase letters and additional symbols through two-character combinations---but this doubles the length of barcodes that use these characters, compounding the density problem. |
Code 39's limitations are not fatal flaws in absolute terms. For simple applications with short identifiers, decent print quality, and adequate label space, Code 39 works well and remains a practical choice. Its self-checking property and unparalleled compatibility make it robust in less controlled printing environments. |
However, as the demand for longer identifiers, smaller labels, and higher first-pass read rates has grown, Code 39's limitations have increasingly outweighed its advantages. The transition to Code 128 and 2D symbologies across logistics, healthcare, and manufacturing represents a market-driven recognition that density and efficiency are paramount in modern data capture. |
For organizations deploying new barcode applications, Code 39 is rarely the optimal choice today. Its limitations are well-understood and well-documented. The lesson of Code 39's history is that in technology, what was once a breakthrough can, over time, become a bottleneck. The symbology that enabled alphanumeric barcoding has been superseded by technologies that address its shortcomings. Yet Code 39's legacy endures---not only in the billions of Code 39 symbols still scanned daily, but in the understanding it gave us of what a barcode symbology must be: efficient, reliable, and capable of encoding the identifiers that connect physical items to digital information. |
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Key Takeaways |
- Code 39 encodes each character with five bars and four spaces, three of which are wide, making it inherently space-inefficient. |
- The quiet zone requirement of 10X on each side adds significant horizontal space to every Code 39 symbol. |
- Code 39 Extended doubles the length of barcodes containing lowercase letters or extended ASCII characters. |
- Across healthcare, defense, automotive, logistics, and government, Code 39's limitations have caused operational friction and driven transitions to more efficient symbologies. |
- Code 39 remains viable for short identifiers, low-volume applications, and environments requiring compatibility with legacy systems. |
- The transition to Code 128 and 2D symbologies is driven by the need for higher density, smaller labels, and better scanning reliability. |
cs@easiersoft.com