Barcode Generator

What the Barcode Generator Does

Enter a part number, asset tag or label text and the barcode redraws instantly underneath, with the human-readable text printed below the bars. Lowercase is converted to uppercase and any unsupported character is dropped, because standard Code 39 only carries 43 symbols. Download gives you an SVG file.

Code 39 is 'discrete' and 'self-checking': every character is encoded on its own from five bars and four spaces, three of which are wide. That simple structure is easy for even basic scanners to read, which is why Code 39 has been a workhorse for asset tags, ID badges and warehouse labels for decades.

How It Works

Each character maps to a fixed nine-element pattern — five bars and four spaces, with exactly three of the nine wide (hence '3 of 9'). The tool draws narrow elements two pixels wide and wide elements three times that, a 3:1 ratio that sits at the top of the standard's allowed 2:1 to 3:1 range for crisp, forgiving scanning.

Your text is framed with the * start and stop characters, characters are separated by a one-unit gap, and the whole symbol is emitted as inline SVG. Because SVG is vector, you can drop the file into a label template and scale it without the bars turning fuzzy.

Generation algorithm

1. Clean the input. Convert to uppercase and drop anything outside Code 39's 43-character set: 0–9, A–Z, space, and hyphen, period, dollar, slash, plus and percent.
2. Frame the data. Wrap the text in the * start and stop characters that every Code 39 reader looks for.
3. Map each character. Look up each character's nine-element pattern — five bars, four spaces, three of them wide.
4. Size the elements. Draw narrow bars at 2 px and wide bars at 6 px (a 3:1 ratio), with a one-unit gap between characters.
5. Emit SVG. Render the bars plus the human-readable text as vector SVG and offer it for download.

Technical Details

Standards & references

• ISO/IEC 16388 — the international standard for the Code 39 symbology — character patterns, bar ratios and the optional check digit.
• Code 39 character set — 43 symbols — digits, uppercase letters and a handful of punctuation; lowercase and full ASCII need the non-standard Full ASCII extension.
• Mod-43 check digit — an optional self-check character that some systems such as LOGMARS and HIBC require; this tool does not add one.

Accuracy & Limitations

No check digit is added. Code 39 is self-checking at the character level, so many systems do not need one — but if your scanner or standard (LOGMARS, HIBC) expects the mod-43 check character, this output will not include it.

Uppercase only. Type lowercase and it is converted; characters outside the 43-symbol set are silently dropped. Lowercase or the full ASCII range needs the Full ASCII extension, which this tool does not implement.

Code 39 is low-density — each character takes a fair amount of width, so long values produce wide barcodes. For more data in less space, Code 128 or numeric EAN/UPC pack tighter; this tool only makes Code 39.

Leave a quiet zone — a clear margin of at least ten narrow-bar widths — on each side, and do not shrink the height too far, or scanners may miss it. The SVG is just the symbol plus its text.

It encodes exactly what you type; it does not look a value up or check it against any database. A barcode is a label, not proof that the code is registered anywhere.

Real-World Use Cases

When to use it — and when not to

Selling at retail? Those barcodes are EAN-13 or UPC, issued through GS1. Need more data in less width, or lowercase? Code 128 is denser. Want a 2-D code for a URL? Use the QR code generator.

Frequently Asked Questions

References

• ISO/IEC 16388:2023 — Code 39 bar code symbology (ISO)
• Code 39 symbology — introduction and character set (OnBarcode)
• Code 39 Full ASCII (Seagull Scientific Barcode Guide)

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