Check digit calculator
The last digit of a UPC or EAN is worked out from all the digits before it. GS1 applies one sum to every number from 8 to 18 digits long. Type a number and this calculator finds the digit or tests it, with every step laid out.
2
The check digit is 2. The full number is 036000291452.
The number loaded at the start is the one GS1 uses in its own check digit example. A right check digit never makes a number yours to print on goods for sale.
| Digit | Step | Result |
|---|---|---|
| 0 | x 3 | 0 |
| 3 | x 1 | 3 |
| 6 | x 3 | 18 |
| 0 | x 1 | 0 |
| 0 | x 3 | 0 |
| 0 | x 1 | 0 |
| 2 | x 3 | 6 |
| 9 | x 1 | 9 |
| 1 | x 3 | 3 |
| 4 | x 1 | 4 |
| 5 | x 3 | 15 |
| Total | 58 |
58 rounded up to the next ten is 60, and 60 minus 58 is 2.
Opening digits 003: GS1 US. Companies license numbers in this range through GS1. Use it only if your company holds the license for this exact number. The prefix shows which GS1 office issued the license, and GS1 is clear that it does not show where a product was made.
By the UPC Generator team. The answers match GS1's two published check digit examples and the published ISBN and Luhn examples. Last updated 4 November 2026. How UPC Generator pages are made.
The GS1 sum, from GS1's own examples
Every GS1 number uses one method. Start at the digit next to the check digit and multiply by 3, then by 1, then by 3 and so on, moving left. Add the results. The check digit is whatever brings the total up to the next multiple of ten.
GS1 publishes this 18 digit example. For 37610425002123456, the products are 9, 7, 18, 1, 0, 4, 6, 5, 0, 0, 6, 1, 6, 3, 12, 5 and 18, which total 101. The next ten is 110, so the check digit is 9.
Its 13 digit example starts from 629104150021. The total is 57, the next ten is 60, and the check digit is 3. Note that the ISBN-13 weights begin with 1 on the left, because counting from the right is what matters. On a 12 digit body the leftmost weight is 1, and on an 11 digit UPC body it is 3.
Number types and how each one works
| Type | Digits before the check digit | Method |
|---|---|---|
| UPC-A, GTIN-12 | 11 | GS1 sum |
| EAN-13, GTIN-13 | 12 | GS1 sum |
| GTIN-14, ITF-14 | 13 | GS1 sum |
| EAN-8, GTIN-8 | 7 | GS1 sum |
| GLN, for locations | 12 | GS1 sum |
| SSCC-18, for pallets and shipments | 17 | GS1 sum |
| ISBN-13 | 12 | GS1 sum |
| ISBN-10 | 9 | Weights 10 down to 2, divide by 11 |
| Luhn | Any | Double every other digit, add digits |
| Code 39 | Any | Add character values, divide by 43 |
When a number fails
If the digit is wrong, one of three things happened. A digit may have been mistyped, two neighbors may have been swapped, or the number was never valid to begin with. The calculator shows what the last digit should be if the rest is right, but it cannot tell you which of those happened. Check the source before you print, because replacing the last digit of a mistyped number gives you a valid-looking wrong number.
A pass shows only that the digits fit together, and nothing about whether the number was ever issued. Anyone can make up 11 digits and calculate the twelfth. Walmart Marketplace, for one, checks GS1's records as well.
ISBN-10, Luhn and Code 39
ISBN-10 weights its nine digits 10 down to 2, totals them, and picks the check value that makes the total divide by 11. For 0-306-40615, the check digit is 2. Its modern form, 978-0-306-40615-7, is an ISBN-13 and uses the GS1 sum.
Luhn doubles every second digit from the right and subtracts 9 from anything above 9, then adds the lot. It protects many ID and account numbers, and the published example 7992739871 gets check digit 3. The Code 39 check is a plain sum of character values divided by 43, so CODE39 gets W, as the Code 39 generator shows.
From a number to a barcode
Once the number is right, the Make this barcode button carries it over to the matching tool. A UPC goes to the UPC generator, an EAN to the EAN-13 generator, and a 14 digit number to the ITF-14 carton tool. If you need a number in the first place, how to get a UPC code covers the licensed route.
Why the last digit exists
Once the digit is right, how to make a barcode takes the number through to a printed symbol. That sum is one of several schemes that do the same job on credit cards, bank routing numbers and book numbers. What a check digit is compares them and shows the one kind of typo the retail scheme cannot catch.
Check digit questions
How do I calculate a UPC check digit?
Starting from the digit next to the check digit, multiply alternately by 3 and 1. Add the results, then subtract from the next multiple of ten. For 03600029145 the total is 58, so the check digit is 2.
Does a correct check digit mean a real product?
No. It only shows the digits are consistent. Any 11 digits can be given a valid check digit, so it says nothing about whether the number was issued or who holds it. The Verified by GS1 lookup can tell you which company a licensed number belongs to.
What errors does a check digit catch?
The GS1 sum catches every single wrong digit, and most swaps of neighboring digits. It misses a swap when the two digits differ by exactly 5, such as 16 and 61, because both give the same total.
Why does ISBN-10 sometimes end in X?
ISBN-10 divides by 11, so the check value can be 10, and a single digit cannot show that. X stands for 10. ISBN-13 uses the GS1 sum and always ends in a digit from 0 to 9.
Is GTIN-14 calculated the same way as UPC?
Yes. All GS1 numbers use the same 3 and 1 weights, counted from the right. That is why a carton number gets a new check digit once a pack digit goes on the front.
6 source documents
- GS1: How to calculate a check digit manually, fetched 2 November 2026
- GS1: General Specifications, Release 26.0, section 7.9, fetched 2 November 2026
- GS1: Verified by GS1 lookup, fetched 2 November 2026
- Walmart Marketplace: Choose a product identifier, fetched 2 November 2026
- Wikipedia: ISBN, check digit examples, fetched 2 November 2026
- Wikipedia: Luhn algorithm, worked example, fetched 2 November 2026