Code 128 is a high-density, variable-length linear barcode standard defined in ISO/IEC 15417. It supports all 128 standard ASCII characters across three internal sets:

• Subset A: High-priority control characters (NUL to US), uppercase letters, punctuation, and digits.
• Subset B: Complete standard alphanumeric ASCII including uppercase, lowercase letters, symbols, and numbers.
• Subset C: High-density dual-digit numeric compaction where two numeric digits (00-99) are packed into a single 11-module barcode symbol, cutting barcode label width by up to 50%.

Our client-side engine automatically analyzes your input payload and seamlessly switches between Subsets B and C to guarantee minimum physical footprint and maximum optical scanning speed.

Retail point-of-sale optical scanners rely on the GS1 standard Modulo-10 Check Digit to prevent misreads caused by smudges, scratches, or damaged packaging. The check digit is the final digit calculated as follows:

1. Count digit positions from right to left (excluding the check digit itself), starting with weight 3, then alternating weight 1 and weight 3.
2. Multiply each payload digit by its assigned weight and sum the products.
3. The check digit is the smallest integer needed to round this sum up to the nearest multiple of 10: (10 - (sum % 10)) % 10.

If you enter 12 digits for an EAN-13, our tool computes and appends the 13th digit automatically.

A barcode's Quiet Zone is the blank, unprinted margin on the left and right sides of the symbol. Optical laser and CCD imaging barcode scanners need this high-contrast blank space to calibrate their optical baseline sensitivity before reading the first start bar.

According to GS1 standards, the minimum required quiet zone is 10 times the narrow bar width (or at least 2.5 mm). Always ensure high contrast (dark black bars against a bright white background) without any text, graphics, or borders encroaching on the quiet zones.

Direct thermal and thermal transfer printers (such as Zebra, Brother, Rollo, and Dymo) print using discrete thermal printhead pins. Printing low-resolution images with anti-aliasing can cause sub-pixel grey blurring, leading to fuzzy bar edges and scanner decode failures.

For best results:

• Use our Download SVG Vector button for infinite resolution rendering on standard vector desktop publishing software (Illustrator, InDesign, Word).
• Use our Download PNG (300 DPI) button, which uses crisp nearest-neighbor rasterization with zero anti-aliasing blur.
• Keep the narrow bar module width at integer multiples (2px, 3px) to match physical thermal printer dots.

All barcode bit-pattern calculations, checksum validations, SVG DOM generation, and PNG rasterizations occur entirely inside your browser using pure client-side JavaScript. Zero serial numbers, inventory SKUs, customer tracking IDs, or confidential product data are ever sent over the internet to any external server.