The UPC-A barcode includes seven basic elements:
- A leading quiet zone at least the width of 10 narrow bars.
- The start character (guard pattern).
- Six symbol characters.
- The center character (guard pattern).
- Six symbol characters with a check digit.
- The stop character (guard pattern).
- A trailing quiet zone.
The guard patterns noted above occur at the start, stop, and center of a UPC-A symbol. They are typically a greater height than the surrounding symbol bars and follow a specific pattern. For the start and stop bars, the pattern is always narrow bar, narrow space, narrow bar. For the center guard bars, the pattern is always narrow space, narrow bar, narrow space, narrow bar, narrow space.
The UPC-A barcode also uses four widths for bars and spaces, which allows characters to be encoded using only two bars and two spaces, which is the fewest number required of any barcode type.
Two add-on symbols — five digit or two digit — are also available for UPC-A barcodes. These add-ons always occur to the right of the primary symbol and are used to denote information such as the date or the MSRP on products. These add-ons do not contain a start or stop character.