π·οΈ GTIN Check Digit Calculator
The GS1 mod-10 check digit.
Computed check digit
Estimates for planning only, not financial advice.
Every GTIN barcode ends with a check digit computed by the GS1 mod-10 algorithm, catching mis-scans and typos before they corrupt inventory. For the 11 digits 03600029152, the check digit is 0, making the full GTIN-12 036000291520. Print the wrong digit and scanners reject the label.
How to Use This Calculator
Enter the 11 digits without the check digit to compute it, or all 12 digits to see the full code confirmed. The calculator applies the GS1 algorithm step by step.
Enter 11 digits (to compute) or 12 digits (to confirm).
Read the check digit and the complete GTIN-12.
Use it on packaging artwork and marketplace listings. For pricing math on the products behind the barcodes, our unit price calculator compares value.
The GS1 Check Digit Algorithm
Weighting alternate digits by 3 catches the most common human errors: single-digit typos always change the check, and most adjacent transpositions do too. The algorithm is identical across GTIN-8, 12, 13, and 14; only the length changes. Marketplaces like Amazon validate the check digit on listing creation, so a bad digit blocks the listing before a human ever sees it.
Worked Example
Digits 03600029152. From the right: positions 1,3,5,7,9,11 hold 2,1,2,0,6,0, summing to 11, times 3 is 33. Even positions hold 5,9,0,0,3, summing to 17. Total: 50. 50 mod 10 is 0, so the check digit is (10 - 0) mod 10 = 0. Full code: 036000291520. Try a transposition: swapping two adjacent digits changes the weighted sum by a multiple of the digit difference times 2, which the mod-10 check catches in most cases.
Barcode Gotchas
The check digit validates the number, not the product: it cannot tell you the digits belong to your item, only that they are self-consistent. Leading zeros matter; dropping the leading zero of a GTIN-12 breaks systems expecting 12 digits. And UPC versus EAN: a 12-digit GTIN with a leading zero is the same product as the 13-digit EAN, a frequent source of duplicate listings. Get GS1-registered prefixes rather than inventing numbers; made-up barcodes collide with real products eventually.
My advice for sellers: compute the check digit in your SKU system, not by hand at the printer. One wrong digit on 10,000 labels is an expensive lesson in why the algorithm exists. Validate every code with this calculator before it touches artwork.
Estimates for planning only, not financial advice.
Frequently Asked Questions
What is a GTIN check digit?
The final digit of a GS1 barcode, computed from the other digits by a mod-10 algorithm. It lets scanners detect misreads and typos automatically. Every GTIN-8, 12, 13, and 14 carries one.
How is the GS1 check digit calculated?
From the right, multiply digits in odd positions by 3 and even positions by 1, sum them, and take (10 - sum mod 10) mod 10. The weighting catches single-digit errors and most transpositions.
What is the difference between UPC and GTIN-12?
UPC-A is the American name for the 12-digit barcode; GTIN-12 is the GS1 global name. They are the same structure. EAN-13 is the 13-digit international sibling.
Can I make up my own barcode numbers?
Technically yes, practically no. GS1 licenses unique company prefixes; invented numbers collide with real products and get flagged by marketplaces. Amazon and retailers require legitimate GS1 codes.
Why does Amazon reject my barcode?
Usually a wrong check digit, an unregistered prefix, or a duplicate of another brand's code. Validate the check digit here first, then confirm the prefix is yours in GS1.
Do I need a different check digit for each size variant?
Yes. Each distinct sellable unit, each size, color, and pack count, needs its own GTIN with its own check digit. Variants sharing a code corrupt inventory and listings.
What is a GTIN-14?
The 14-digit code for cases and pallets, built from the inner GTIN plus a packaging indicator. Same check-digit algorithm, longer number. Used in wholesale and logistics.
Can the check digit detect all errors?
No. It catches all single-digit substitutions and most transpositions, but some error pairs cancel out. It is a safety net, not a guarantee, which is why prefix registration still matters.
What should I do if two products share a GTIN?
Assign a new GTIN to one of them immediately and update every listing and label. Shared GTINs corrupt inventory counts and marketplace catalogs, and the cleanup cost grows with every unit shipped.
Are QR codes replacing barcodes?
For consumer engagement, increasingly; for checkout and supply chain, not soon. GS1 is pushing 2D barcodes at point of sale, but the GTIN inside them, check digit included, remains the identifier.
How do I get a GS1 company prefix?
License one from GS1 in your country; pricing scales with how many GTINs you need. The prefix guarantees global uniqueness, which is what retailers and marketplaces actually require.