Barcode Generator for Code 128, EAN-13, UPC-A

Which barcode type do you need?

Use Code 128 for anything internal: shipping and warehouse labels, asset tags, library cards, order numbers, serials. It encodes any ASCII text (letters, digits, punctuation and even control characters such as tab), it is compact, and every common handheld and phone scanner reads it.

Use EAN-13 or UPC-A only for products sold through retail. These are GS1 numbers: the first digits are a company prefix that a business licenses from its national GS1 organisation, and the shop's point-of-sale system looks the number up in its product database. Generating the barcode image is free and this page does it, but making up a number does not give you a valid product code, and marketplaces such as Amazon check registered prefixes. UPC-A is the 12-digit form used in the US and Canada; EAN-13 is the 13-digit form used everywhere else and also for books, where the ISBN-13 is the EAN-13 (prefix 978 or 979). A UPC-A number is the same as an EAN-13 with a leading zero, and modern scanners read both.

How the check digit is calculated

EAN-13 and UPC-A end with a check digit so a scanner can catch a misread. Starting from the digit immediately left of the check digit and moving left, multiply the digits alternately by 3 and 1, add the products, and take the amount needed to reach the next multiple of 10. For 400638133393, the weighted sum is 89, so the check digit is 1 and the full EAN-13 is 4006381333931.

Type 12 digits for EAN-13 (or 11 for UPC-A) and this generator appends the check digit. Type the full 13 (or 12) and it verifies the last digit, refusing to draw a barcode with the wrong one and telling you the correct number instead. That catches the most common copy-paste and typing mistakes before anything is printed.

Code 128 has its own check symbol, a weighted sum of every symbol value modulo 103, which is added automatically and is not shown in the text under the bars.

Code 128 code sets and automatic switching

Code 128 has three code sets. Set B covers printable ASCII including lowercase letters, set A covers uppercase letters, digits and control characters, and set C packs two digits into each symbol, so long numbers take half the width. This encoder picks the set for you: it starts in C when the text begins with four or more digits, switches into C for any run of four or more digits in the middle, uses A only when a control character needs it, and uses B for everything else. An odd-length run of digits sends its first digit in the current set before switching, so no digit is wasted.

The encodings were checked against the JsBarcode library's output and decoded back to the original text for strings mixing letters, digit runs and control characters. GS1-128 (FNC1 application identifiers) is not supported; if your carrier requires GS1-128 labels, use their labelling software.

Printing barcodes that scan

Download SVG for print. It is a vector file made of rectangles, so the bars stay exactly the width the symbology defines at any size, which is what scanners need; resizing a low-resolution PNG is the usual cause of fuzzy, unreadable bars. Use PNG (rendered at twice the on-screen size) for documents, spreadsheets and web pages.

Keep the quiet zones, the blank margins at each end. The generated image includes them: 11 modules on the left and 7 on the right of an EAN-13, 9 on each side of a UPC-A and 10 for Code 128. Black bars on a white background are the safest choice. Red bars are invisible to the red lasers most scanners use, and low contrast or a dark background will fail. EAN-13 and UPC-A are designed for a nominal width of about 37 mm; you can print smaller, but test with the scanner that will actually be used.