Code 128 Barcode Generator

What is Code 128?

Code 128 is a compact, high-density barcode that encodes digits, upper- and lower-case letters and common ASCII symbols. It's widely used in shipping, logistics and warehouse labels.

How to create one

Type any text or number. The generator selects the optimal Code Set (A, B or C) automatically to keep the barcode as short as possible, and shows a live preview. Download PNG or SVG, or print directly.

How it works

Code 128 packs data efficiently and includes its own checksum internally, so it's reliable even for longer strings. Numeric-only data compresses especially well using Code Set C.

Where to use it

Shipping labels, asset tags, batch and lot numbers, and internal inventory systems all rely on Code 128 for its density and flexibility.

Scanning and printing tips

Longer data makes a wider barcode — give it room and don't compress horizontally. Keep bars crisp and high-contrast, and test with your target scanner.

Limitations

Code 128 encodes standard ASCII only. Extremely long strings create very wide barcodes that may not fit your label.

Code sets A, B and C

Code 128 encodes the full 128-character ASCII set by switching between three sub-modes. The tool selects them automatically; understanding them explains why the symbol changes width as you type.

Set C is the reason Code 128 is so compact for numbers: a 20-digit value takes 10 symbol characters instead of 20. Automatic mode switches into C whenever four or more digits appear together and switches back afterwards, so ABC12345678 is encoded partly in B and partly in C without you doing anything.

The practical consequence: an even number of digits encodes more compactly than an odd number. A 13-digit value cannot be fully paired, so one digit falls back to single-character encoding. If you are designing a numbering scheme and label width is tight, an even length is free efficiency.

Check character and start/stop patterns

Code 128 always carries a modulo-103 check character, and it is not optional and not shown in the human-readable text. It is calculated from the start character and the weighted positions of the data, and the encoder handles it — there is nothing to enable and nothing you can get wrong.

Every symbol also has a start character that declares the initial code set, and a stop pattern with a distinctive 13-module bar that lets a scanner tell which end it is reading from. This is why a Code 128 scans correctly upside down, and why the encoded symbol is always wider than the character count alone suggests: expect roughly 11 modules per symbol character, plus 35 for start, check and stop, plus a 10-module quiet zone at each side.

For a 10-character value that works out to about 145 modules of symbol plus 20 of quiet zone. At a 0.25 mm X-dimension that is roughly 41 mm wide — worth checking against your label before you order 10,000 of them.

Code 128 or Code 39?

Both encode alphanumeric data and both are free to use with no registration. They are not interchangeable in practice.

Choose Code 128 for anything new: inventory, asset tags, shipping references, internal SKUs. It is denser, safer and carries lowercase.

Choose Code 39 only when something you cannot change requires it — an old scanner, a military or automotive standard that specifies it, or a partner's existing label spec. Longer comparison: Code 128 vs Code 39.