Linear symbology
UPC-A
UPC-A is the 12-digit retail barcode used in the United States and Canada. Eleven digits carry the company prefix and item reference and the twelfth is a check digit; it is a GTIN-12, and the same underlying number can be expressed as an EAN-13 by prefixing a zero.
Specification
These are the values the editor enforces while you design, not figures collected from elsewhere — the same numbers its quiet-zone and resolution checks run on.
| Property | Value | In context |
|---|---|---|
| Minimum X-dimension | 0.264 mm | 0.0104 in · 10 thou |
| Quiet zone | 9 modules | 2.38 mm at the minimum X-dimension |
| Dimensionality | Linear (1D) | Read by laser or imager |
UPC-A at 203, 300 and 600 dpi
A printer can only place whole dots, and 0.264 mm is not a whole number of them at any of these resolutions. What changes is how much a single dot of rounding costs you as a share of the narrow bar.
| Resolution | Narrow bar in dots | Printed as | Rounding error |
|---|---|---|---|
| 203 dpi | 2.11 | 2 dots | 5% |
| 300 dpi | 3.12 | 3 dots | 4% |
| 600 dpi | 6.24 | 6 dots | 4% |
What UPC-A encodes
Exactly 12 digits. Eleven of data and one computed check digit. No letters, no punctuation, no variable length.
Where it is used
- Retail products sold through US and Canadian points of sale
- Grocery and general merchandise where a trading partner specifies UPC
Check digit
Starting from the rightmost data digit and working left, multiply the digits alternately by 3 and 1, add the results, then subtract the total from the next multiple of ten. The remainder is the check digit. The editor computes it for you, and accepts the value either with or without it.
How UPC-A fails in practice
- Printing below the 80% magnification floor, exactly as with EAN-13. The narrow bar stops resolving and a symbol that looks clean on screen fails intermittently at the till.
- Truncating the height to fit a design. A shortened symbol can only be scanned along a narrower band, which matters at a checkout where the operator sweeps the pack rather than aiming.
- Placing the number's human-readable digits inside the quiet zone, which is a layout habit carried over from designing without a scanner in mind.
When to use something else
Questions about UPC-A
- Is a UPC-A the same as an EAN-13?
- They carry the same underlying GTIN. A UPC-A is a GTIN-12, and prefixing it with a single zero gives the equivalent GTIN-13. Modern retail scanners read both, so the choice is usually about what a trading partner specifies rather than what a scanner can handle.