The UPC-E format contains six key elements:
- A leading quiet zone at least 10x the width of one narrow bar.
- A start character (guard pattern).
- Six symbol characters including the check digit.
- A stop character (guard pattern).
- A trailing quiet zone.
The two guard patterns used by the UPC-E symbol are typically longer than the surrounding bars. This creates a small “notch” under the barcode which is often used to print human-readable text. The guard patterns always follow a specific format:
- Start character — narrow bar, narrow space, narrow bar
- Stop character — narrow space, narrow bar, narrow space, narrow bar, narrow space
UPC-E barcodes only encode numeric digits 0-9 and also use a check digit based on the modulo 10 (mod 10) algorithm. They can also be paired with two- or five-digit add-on symbols that appear to the right of the original barcode and are used to denote specific pricing or date information.