Barcode Generator

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Code 39 barcode generator

Code 39 dates from the 1970s and survives on badges, library cards, labs and industrial registries because it is simple and needs no check character. The trade-off is space: the same data takes much more width than in Code 128, and the alphabet is small.

Alphabet, structure of each character and the modulo 43

The name "3 of 9" describes the structure: every character has 9 elements (5 bars and 4 spaces) and exactly 3 of them are wide. The alphabet has 43 characters: the digits 0 to 9, uppercase letters A to Z, and the symbols hyphen, period, space, dollar, slash, plus and percent. The asterisk is reserved: the generator adds it at the start and end, so you cannot use it in the data. Lowercase letters are converted to uppercase, with a notice on screen. Here a wide bar is 3 modules, the ratio most tolerant of print flaws.
Each character takes 15 modules (3 wide of 3 and 6 narrow of 1) plus 1 module of gap between characters. A value of n characters, with start and stop, therefore measures (n + 2) x 16 - 1 modules: BADGE-0042 has 10 characters and 12 counting the asterisks, or 191 modules. The same data in Code 128 takes 134, because Code 128 packs the four trailing digits into two symbols; a digits-only value such as 12345678 takes 159 modules in Code 39 and 79 in Code 128, half as many.
The check character is optional, but it exists: the modulo 43 adds up the value of each character (0 to 9 are worth 0 to 9, A to Z are 10 to 35, and the symbols 36 to 42) and uses the remainder of division by 43 as an extra character. For CODE39 the sum is 75, the remainder is 32 and the character is W. Turn the option on only if the destination system expects that character, because a scanner configured without a check returns the W as part of the data.

Four inputs and what comes out

Stock code with a hyphen

Input: ESTOQUE-0042
Expected output: 223 módulos (156 em Code 128)

14 characters with the asterisks, 16 modules each, minus the last gap.

Event badge

Input: BADGE-0042
Expected output: 191 módulos (134 em Code 128)

The same rule as the previous example with 12 characters counted.

Modulo 43 check turned on

Input: CODE39
Expected output: CODE39W

Sum 75, remainder 32 in the alphabet table, which maps to the letter W.

Asterisk in the data

Input: A*B
Expected output: Recusado

The asterisk is the start and stop character, and inside the data it would confuse the scanner.

Full tool FAQ

Which barcode should I use for a product sold in stores?

EAN-13 in most of the world, UPC-A in the United States and Canada, and EAN-8 on very small packages. Books use ISBN-13. The number has to come from your country's GS1 office; this tool only draws the bars.

Is an EAN-13 generated here a valid product code?

PNG or SVG: which one should I download?

How is the EAN check digit calculated?

Code 128 or Code 39?

When should I use ITF-14?

Why does my scanner not read the printed code?

Does the code data go to any server?

Frequently asked questions

Does Code 39 accept lowercase letters and accents?

No. The standard alphabet has only uppercase letters, digits and seven symbols. The tool converts lowercase to uppercase and refuses accents. There is a Code 39 Extended that pairs two characters to cover ASCII, but many scanners do not decode it.

What is the character limit?

The tool accepts up to 40 data characters. The standard sets no ceiling, but each character costs 16 modules, and a very long code gets too small to fit a readable label.

Code 39 or Code 128 for new labels?

Code 128 in most cases, for the smaller size and the full alphabet. Use Code 39 when the receiving system, the scanner or the customer requires it.

Does the text under the bars show the asterisks?

No. The text shows only the data (and the check character, if on). The asterisks are in the bars, and the scanner usually strips them before returning the value.

Next steps

Alphabet, structure of each character and the modulo 43

The name "3 of 9" describes the structure: every character has 9 elements (5 bars and 4 spaces) and exactly 3 of them are wide. The alphabet has 43 characters: the digits 0 to 9, uppercase letters A to Z, and the symbols hyphen, period, space, dollar, slash, plus and percent. The asterisk is reserved: the generator adds it at the start and end, so you cannot use it in the data. Lowercase letters are converted to uppercase, with a notice on screen. Here a wide bar is 3 modules, the ratio most tolerant of print flaws.

Each character takes 15 modules (3 wide of 3 and 6 narrow of 1) plus 1 module of gap between characters. A value of n characters, with start and stop, therefore measures (n + 2) x 16 - 1 modules: BADGE-0042 has 10 characters and 12 counting the asterisks, or 191 modules. The same data in Code 128 takes 134, because Code 128 packs the four trailing digits into two symbols; a digits-only value such as 12345678 takes 159 modules in Code 39 and 79 in Code 128, half as many.

The check character is optional, but it exists: the modulo 43 adds up the value of each character (0 to 9 are worth 0 to 9, A to Z are 10 to 35, and the symbols 36 to 42) and uses the remainder of division by 43 as an extra character. For CODE39 the sum is 75, the remainder is 32 and the character is W. Turn the option on only if the destination system expects that character, because a scanner configured without a check returns the W as part of the data.

Four inputs and what comes out

Stock code with a hyphen

Input: ESTOQUE-0042
Expected output: 223 módulos (156 em Code 128)

14 characters with the asterisks, 16 modules each, minus the last gap.

Event badge

Input: BADGE-0042
Expected output: 191 módulos (134 em Code 128)

The same rule as the previous example with 12 characters counted.

Modulo 43 check turned on

Input: CODE39
Expected output: CODE39W

Sum 75, remainder 32 in the alphabet table, which maps to the letter W.

Asterisk in the data

Input: A*B
Expected output: Recusado

The asterisk is the start and stop character, and inside the data it would confuse the scanner.

Full tool FAQ

Which barcode should I use for a product sold in stores?

Is an EAN-13 generated here a valid product code?

PNG or SVG: which one should I download?

How is the EAN check digit calculated?

Code 128 or Code 39?

When should I use ITF-14?

Why does my scanner not read the printed code?

Does the code data go to any server?

Frequently asked questions

Does Code 39 accept lowercase letters and accents?

What is the character limit?

The tool accepts up to 40 data characters. The standard sets no ceiling, but each character costs 16 modules, and a very long code gets too small to fit a readable label.

Code 39 or Code 128 for new labels?

Code 128 in most cases, for the smaller size and the full alphabet. Use Code 39 when the receiving system, the scanner or the customer requires it.

Does the text under the bars show the asterisks?

No. The text shows only the data (and the check character, if on). The asterisks are in the bars, and the scanner usually strips them before returning the value.