EAN-13 and UPC-A are the two dominant retail barcode number systems printed on almost every product sold worldwide. Both end in a mod-10 check digit that barcode scanners use to detect misreads in real time. This free validator auto-detects the type by digit count and runs the correct checksum — and shows you the expected correct check digit when one is wrong.
How it works
Both systems use a weighted modulus-10 check digit, but with mirrored weight patterns:
- EAN-13 (13 digits): alternate weights
1, 3, 1, 3, ...from the left — odd positions ×1, even positions ×3. Sum all 13 weighted digits; the barcode is valid when the total is divisible by 10. - UPC-A (12 digits): alternate weights
3, 1, 3, 1, ...from the left — odd positions ×3, even positions ×1. Sum all 12 weighted digits; valid when divisible by 10.
To compute what the check digit should be: weight the leading 12 (EAN-13) or 11 (UPC-A) digits, sum them, and take check = (10 − (sum mod 10)) mod 10.
Worked example — EAN-13 validation
Barcode: 4006381333931 (13 digits)
Position: 1 2 3 4 5 6 7 8 9 10 11 12 13
Digit: 4 0 0 6 3 8 1 3 3 3 9 3 1
Weight: 1 3 1 3 1 3 1 3 1 3 1 3 —
Product: 4 0 0 18 3 24 1 9 3 9 9 9
Sum = 4+0+0+18+3+24+1+9+3+9+9+9 = 89 + check digit 1 = 90 ✓ (divisible by 10)The barcode is valid. The check digit 1 makes the total exactly 90.
The UPC-A / EAN-13 relationship
A UPC-A barcode is structurally identical to an EAN-13 with a leading zero prepended. The barcode 036000291452 (UPC-A) is the same product as 0036000291452 (EAN-13). This is why GS1 describes UPC-A as GTIN-12 — it is a subset of the Global Trade Item Number system, where EAN-13 is GTIN-13.
When a scanner reads a UPC-A, it can expand it to a 13-digit EAN-13 by prepending a 0, allowing the same database to handle both formats.
Structure of an EAN-13 number
| Digits | Component | Notes |
|---|---|---|
| 1–3 | GS1 Company Prefix (country or issuer) | Not a “country of origin” — it identifies the GS1 member |
| 4–12 | Company and product code | Length split depends on prefix length assigned |
| 13 | Check digit | Computed from the first 12 |
Prefixes starting with 50 are assigned to the UK. Prefixes 00–09 are US and Canada (UPC/EAN). Prefixes 978–979 are for books (ISBN). Prefix 977 is for periodicals (ISSN).
Common uses for this validator
- E-commerce data entry: Verify barcode digits before uploading a product catalogue to Amazon, eBay, or Shopify.
- Inventory management: Catch OCR transcription errors when barcodes are manually entered.
- Print pre-flight: Confirm a barcode’s check digit matches before sending artwork to press.
- Software development: Test barcode parsing code against known-valid and known-invalid inputs.
All validation runs locally in your browser — no barcode data is sent to a server.