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Code 39 is one of the oldest barcodes still in wide use. It encodes uppercase letters, digits and a few symbols, and it’s simple enough to print with a font, which is a large part of why it lasted.

Decode one

Scan or paste a barcode and see every part of it.

Make one

Generate a valid barcode from fields.

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Where you’ll see it

  • Manufacturing and automotive parts labels.
  • Government and defense, on equipment and supply labels.
  • Healthcare, on some specimen, patient and supply labels.
  • ID badges and asset tags, often printed with a barcode font.

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Anatomy

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Characters

Each character is nine elements, five bars and four spaces, and exactly three of the nine are wide. That’s where the name comes from. A narrow gap separates one character from the next, so each one can be read on its own. A wide element is 2 to 3 times the width of a narrow one.

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43 characters

There are no lowercase letters.

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Start and stop asterisks

Every Code 39 barcode starts and ends with an asterisk. Labels made with a barcode font often print the asterisks in the text too, but scanners don’t send them.

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Full ASCII

Full ASCII mode reaches all 128 ASCII characters by encoding the missing ones as pairs. A lowercase a, for example, is +A. Nothing in the barcode says it uses Full ASCII, so the scanner has to be set up for it.

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Check character

Code 39 doesn’t require a check character, and most Code 39 barcodes don’t have one. Where it’s used, it’s the last character before the stop asterisk, calculated with mod-43. The example’s check character is J. Because it’s optional and nothing marks it, the scanner and your app both have to be told whether to expect it. See Check digits.
  • Code 93: a denser successor with two required check characters.
  • Code 128: denser again, with lowercase letters and digit compression. The usual choice for new labels.

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Gotchas

  • Asterisks on the label, none in the scan. See asterisks around the text.
  • One extra character. The barcode has a check character the label doesn’t show. See a missing last digit.
  • +A instead of a. The barcode uses Full ASCII and the scanner isn’t set up for it, or the other way round.
  • Wide barcodes. Code 39 is the least dense barcode in common use. Long values make labels too wide to scan comfortably.

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Scanning it in your app

See Validation.

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Specification

  • ISO/IEC 16388: the Code 39 barcode specification.