Editing Universal Product Code (section)

=== Formatting ===
UPC-A barcodes can be printed at various densities to accommodate a variety of printing and scanning processes. The significant dimensional parameter is called x-dimension (width of single module element). The width of each bar (space) is determined by multiplying the x-dimension and the module width (1, 2, 3, or 4 units) of each bar (space). Since the guard patterns each include two bars, and each of the 12 digits of the UPC-A barcode consists of two bars and two spaces, all UPC-A barcodes consist of exactly (3&nbsp;×&nbsp;2)&nbsp;+&nbsp;(12&nbsp;×&nbsp;2)&nbsp;=&nbsp;30 bars, of which 6 represent guard patterns and 24 represent numerical digits.

The x-dimension for the UPC-A at the nominal size is 0.33&nbsp;mm (0.013"). Nominal symbol height for UPC-A is 25.9&nbsp;mm (1.02"). The bars forming the S (start), M (middle), and E (end) guard patterns, are extended downwards by 5 times x-dimension, with a resulting nominal symbol height of 27.55&nbsp;mm (1.08"). This also applies to the bars of the first and last numerical digit of UPC-A barcode. UPC-A can be reduced or magnified anywhere from 80% to 200%.

A quiet zone, with a width of at least 9 times the x-dimension, must be present on each side of the scannable area of the UPC-A barcode.<ref>{{cite web|url=http://www.codeproject.com/KB/graphics/upc_a_barcode.aspx|title=Drawing UPC-A Barcodes with C#|author=rainman_63|date=6 April 2005|work=codeproject.com|access-date=7 July 2011|archive-date=29 August 2011|archive-url=https://web.archive.org/web/20110829061253/http://www.codeproject.com/KB/graphics/upc_a_barcode.aspx|url-status=live}}</ref><ref>{{cite book|url=https://books.google.com/books?id=yrELQAAACAAJ|title=UPC Symbol Specification Manual |year=1986 |publisher=[[Uniform Code Council]]}}</ref> For a GTIN-12 number encoded in a UPC-A barcode, the first and last digits of the [[human-readable interpretation]] are always placed outside the symbol in order to indicate the quiet zones that are necessary for UPC barcode scanners to work properly.