The symbol comprises the following elements:

• Leading quiet zone

• Guard pattern (start character)

• Six symbol characters

• Center guard pattern (center character)

• Six symbol characters, including check digit

• Guard pattern (stop character)

• Trailing quiet zone

Guard bars. The guard bars are the start, stop, and center characters in an ISBN-13 symbol.

The start and stop characters are identical to each other. They are made up of three modules as follows:

narrow bar

narrow space

narrow bar

The center character is made up of five modules as follows:

narrow space

narrow bar

narrow space

narrow bar

narrow space

The bars for these characters are longer than the bars that encode data, and they are sometimes referred to as security bars.

This symbology supports all numeric digits (0-9).

ISBN-13 contains a check digit that is based on the modulo 10 (mod 10) algorithm.

As with EAN-13, a five-digit EAN-5 add-on symbol (supplemental barcode) is available for ISBN-13 that is typically used to encode a publisher's suggested retail price. A human readable interpretation is always included in the add-on symbol.