1.5. Technical Detail

The UPC has only numerals (digital number), without letters (such as ‘A’, ‘B’,… ) or other (control / function ) characters.

Total 12 decimal digits, its format/syntax is:

SLLLLLLMRRRRRRE

In which:

  1. S – Start, E – End

    fixed bit pattern 101

  2. M – Middle

    fixed bit pattern 01010, called guard bars

  3. L – Left, R - Right

    both have 6 digits, each digit is a 7 bits code

So, total bits = S + L + M + R +E = 3 + 7 * 6 + 5 + 7 * 6 + 3 = 95 bits

Since S, M, and E all 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 × 2) + (12 × 2) = 30 bars.

For left digits and right digits:

The first digit L is the prefix.

The last digit R is an error correcting check digit, allowing some errors in scanning or manual entry to be detected.

UPC data structures are a component of GTINs (Global Trade Item Numbers). All of these data structures follow the global GS1 standards.