EAN-13 barcode generator

How an EAN-13 barcode is put together

An EAN-13 (originally European Article Number, now International Article Number) is the barcode that carries a 13 digit GTIN-13. It is drawn on a grid of equal-width columns called modules. Each module is either dark or light, so the whole symbol is a string of bits: a bar is a run of 1s and a space a run of 0s, and a bar can be one to four modules wide. At the nominal size a module is 0.33 mm.

The guards are fixed patterns: 101 at each end and 01010 in the middle. They give a scanner a reference width for one module and mark where each half starts. On a printed label they are drawn longer than the other bars, which is why they poke down between the digits. Between the guards there are always 95 modules, whatever the number.

The three codes: L, G and R

Every digit is drawn as 7 modules: two bars and two spaces. There are three ways to draw each digit. The L code (set A in the specification) is used on the left, R (set C) on the right, and G (set B) is a second choice on the left of an EAN-13. R is L with every module inverted, and G is R read backwards.

• Left codes start with a space, right codes with a bar. Every L and G code begins with 0 and ends with 1; every R code is the other way round.
• Parity tells the sets apart. Each L code has an odd number of dark modules (3 for 0), each G and R code an even number (4 for 0). A scanner that counts them knows which set a digit came from.
• Direction comes free. The first digit after the start guard is always an L code, which is odd. Read backwards, the first code a scanner meets is an R code reversed, which is even, so it knows to flip the symbol round. That is how a checkout scanner reads a product held either way up.

Where the 13th digit hides

Twelve digits get bars, but an EAN-13 has thirteen. The first digit is never drawn. Instead it decides, for each of the six left-hand digits, whether the L or the G code is used, and a scanner reads it back from that pattern. The right half always uses R.

In the default example, 4006381333931, the first digit is 4, so the left half reads LGLLGG: 0 as L, 0 as G, 6 as L, 3 as L, 8 as G, 1 as G. A first digit of 0 gives all L, which is a plain UPC-A; that is how EAN-13 was made to include the older American code without changing any bars.

Working out the check digit

Weight the digits 1, 3, 1, 3 and so on, counting so that the digit next to the check digit gets 3. Add the products, and the check digit is what is needed to reach the next multiple of 10. For an EAN-13 the weights start with 1 on the first digit; for a 12 digit UPC-A they start with 3, which is the same rule seen from the other end.

Because 3 and 1 are both coprime to 10, changing any one digit always changes the sum by something that is not a multiple of 10, so every single-digit mistake is caught. Swapping two neighbouring digits is caught too, unless they differ by exactly 5: 0↔5, 1↔6, 2↔7, 3↔8, 4↔9. Those 5 pairs out of 45 change the sum by a multiple of 10.

UPC-A and EAN-8

UPC-A (Universal Product Code) has 12 digits and is used in the United States and Canada. It is an EAN-13 whose first digit is 0: the bars of UPC-A 036000291452 and EAN-13 0036000291452 are identical. A UPC-A label prints its first and last digits small, outside the bars, and draws those two digits' bars long like the guards.

EAN-8 is the short version for small packs: 8 digits, four each side of the centre guard, all L on the left and all R on the right, so there is no hidden digit. Its 67 modules use the same codes, guards and check digit rule. EAN-8 numbers are allocated separately by GS1, not by shortening an EAN-13.

What the first three digits mean

The first two or three digits of an EAN-13 are a GS1 prefix. It identifies the GS1 member organisation that issued the company prefix to the brand owner. It is not the country where the product was made: a company registered in one country keeps its prefix for goods made anywhere. A few ranges have special uses instead. This table is a selection, not the full list.

Every UPC-A, read as an EAN-13 with a leading 0, falls between 000 and 099. The restricted circulation ranges 020 to 029 and 200 to 299 are for use within a geographic region, with rules set by the local GS1 member organisation (often weighed or priced items labelled in store); 040 to 049 is for use inside a single company. None of them identify a product outside that scope.

Book barcodes: ISBN-10 to ISBN-13

Books use the 978 and 979 prefixes, sometimes called Bookland, and the EAN-13 printed on a book is its ISBN-13. ISBNs have been 13 digits since 2007. An older ISBN-10 converts by putting 978 in front and replacing its check character, which works differently: weights 10 down to 2, modulo 11, with X standing for 10.

Only 978 numbers have an ISBN-10 equivalent; 979 numbers are new and exist only as 13 digits (979-0 is used for printed music, as the ISMN). Magazines and other serials use 977 followed by the first seven digits of their ISSN.

Common mistakes

• Reading the prefix as a country of origin. 400 to 440 means the company prefix came from GS1 Germany, not that the product was made there.
• Using a UPC-A as the first 12 digits of an EAN-13. A 12 digit UPC-A already has its check digit. Typing it into an EAN-13 generator adds a 13th digit and makes a different number; put a 0 in front instead.
• Cropping the quiet zone. The blank margins are part of the symbol. Placing the code against an edge or a line of text can make it unreadable.
• Scaling a small PNG. Stretched pixels make some bars a pixel wider than others. Use the SVG for print, or a PNG at a whole number of pixels per module.
• Inventing numbers for real products. Shops and marketplaces expect a GTIN licensed from GS1. A number that merely has a valid check digit is not registered to anyone; the 200 to 299 range exists for in-store use.

Barcodes are bits drawn as stripes. For the same idea in two dimensions see the QR code generator; for bits as numbers and text, the binary converter and the ASCII table.