### UPC-A

UPC-A Structure (From left to right)
The Number System
Start guard bars, always with a pattern bar+space+bar.
The Manufacturer Code
Center guard bars, with a pattern space+bar+space+bar+space.
The Product Code
End guard bars, always with a pattern bar+space+bar.
The Check Digit

UPC-A (Universal Product Code-A) is of fixed length. It encodes a twelve-digit numeric only number. The final digit is a check digit, which cannot be omitted. The usual height of a UPC-A bar code is one inch. The reduced size is 80% of the nominal size.

UPC-A is a subset of EAN-13. In fact, a UPC-A barcode is an EAN-13 barcode with the first EAN-13 number system digit set to "0". This means that any hardware or software capable of reading EAN-13 is automatically capable of reading UPC-A.

Usually, the number system digit is printed on the left of the barcode, and the check digit on the right; while the manufacturer and product codes are printed just below the barcode, separated by a guard bar.

Both the left and the right guard bar are encoded with 101 (bar space bar).

Usual X dimension is 13 mils. A magnification factor of 0.8 to 2.0 is permitted and, as a result, enables a printable X dimension values range of 10.4 to 24 mils.