Check Digit Calculator

Work out the last digit of a barcode number, or check that a number you have is right. EAN-13, EAN-8, UPC-A, UPC-E, GTIN-14 (ITF-14), SSCC, ISBN-13, ISBN-10 and ISSN, with every step of the sum shown. Paste a whole list to check it in one go and save the results as CSV.

1Pick the code type
2Type the number
3Copy or save

1Pick the code type and what to do

Code type

2Type the digits before the check digit

Digits without the check digit (spaces and hyphens are fine)

Try:

Everything runs in your browser: the numbers you type or paste are never sent anywhere. We count visits and finished downloads (tool name only) with analytics that sets no cookies.

2Paste a list, one number per line

Numbers (up to 10,000 lines). With "Detect from the number", each line is detected on its own.

For each line

Download CSV

#	You typed	Type	Full number	Result

Your list stays in your browser and the CSV is made on your device. We count visits and finished downloads (tool name only) with analytics that sets no cookies.

Same item, other forms

Type a number to see its other forms: ISBN-10 and ISBN-13, UPC-E and UPC-A, and the 14-digit GTIN.

Need the barcode too?

Once the number is right, make a print-ready EAN-13, UPC-A or ITF-14 barcode as SVG or PNG with the Barcode Generator.

How to calculate a check digit

EAN, UPC, GTIN-14, SSCC and ISBN-13 numbers all use the same GS1 method. GS1 says it is "identical for all fixed length numeric GS1 data structures" (GS1 General Specifications, section 7.9.1).

Weight the digits. Start with the digit just left of the check digit and multiply it by 3, the next one left by 1, then 3, 1, 3 and so on.
Add the results.
Round up to a multiple of ten. Subtract the sum from the nearest equal or higher multiple of ten. What is left is the check digit. If the sum is already a multiple of ten, the check digit is 0.

GS1's own example is the GTIN-13 629104150021?. The weighted products add up to 57, the next multiple of ten is 60, and 60 − 57 = 3, so the full number is 6291041500213. Press "GS1 GTIN-13" above to see every step.

Which method each code uses

Code	Digits	Method	Example
EAN-13 / GTIN-13	13	GS1 modulo 10, weights 3 and 1	`6291041500213`
UPC-A / GTIN-12	12	GS1 modulo 10	`012345000058`
EAN-8 / GTIN-8	8	GS1 modulo 10	`73513537`
UPC-E	8	Expand to UPC-A, then GS1 modulo 10	`01234558`
GTIN-14 / ITF-14	14	GS1 modulo 10	`10614141123459`
SSCC	18	GS1 modulo 10	`376104250021234569`
ISBN-13	13	Modulo 10, weights 1 and 3 (the same sum as GS1)	`9789295055124`
ISBN-10	10	Modulo 11, weights 10 down to 2, X for 10	`033028987X`
ISSN	8	Modulo 11, weights 8 down to 2, X for 10	`1050124X`

The examples come from the sources below: GS1's worked examples and UPC-E examples, the ISBN Users' Manual and the ISSN Centre. The EAN-8 and GTIN-14 rows are plain sample numbers that pass the same sum.

ISBN-10 and ISSN: modulus 11

The 2001 ISBN Users' Manual says the ISBN-10 check digit is "calculated on a modulus 11 with weights 10-2, using X in lieu of 10". Multiply the first nine digits by 10, 9, 8 … 2, add them, and take the remainder after dividing by 11. The check digit is 11 minus that remainder, written X when it is 10 and 0 when it is 11. The ISSN works the same way on its first seven digits with weights 8 down to 2, so 1050-124X ends in X.

ISBN-10 to ISBN-13, and back

To turn an ISBN-10 into an ISBN-13, put 978 in front of its first nine digits and work out a new check digit with the modulo 10 method; the old check digit is dropped. The ISBN Users' Manual example is 0-330-28987-X, which becomes 978-0-330-28987-0. Going back only works for ISBNs that start with 978: numbers that start with 979 have no 10-digit form.

UPC-E and UPC-A

UPC-E is a short form of a UPC-A number that starts with 0 and has a run of zeros in set places. GS1 lists four zero-suppression rules; for example 0 12345 00005 8 becomes the UPC-E 0 123455 8. The check digit is always worked out on the full 12-digit number, which this tool expands for you. If a UPC-A number has no UPC-E form, the tool says so.

What a check digit can and cannot tell you

A right check digit means the number is typed consistently: it catches every single wrong digit and most swaps of two neighbouring digits. It does not mean the number has been issued to anyone. GS1 company prefixes and ISBN publisher ranges are given out by GS1 member organisations and ISBN agencies, and this tool does not look anything up.

Sources, read 27 October 2026: GS1 General Specifications Standard, Release 26.0 (January 2026), sections 7.9.1, 5.2.2.3 and 5.2.2.4; GS1, How to calculate a check digit manually; ISBN Users' Manual, 7th edition (2017), Appendix 1, with the ISBN-10 rule and conversion example from the 2001 and 2005 editions; ISSN International Centre, What is an ISSN, and the Library of Congress ISSN check digit page for the 8-to-2 weights. Every worked example on this page is in the tool's automated tests, and all of them pass.

FAQ

How do you calculate a check digit?

For EAN, UPC, GTIN and ISBN-13: multiply the digits by 3 and 1 in turn, starting from the right, add them up, and subtract the total from the next multiple of ten. Type the number above without its last digit and the tool shows each multiplication and the sum.

Where is the check digit on a barcode?

It is always the last digit of the number. On an EAN-13 it is the 13th digit, on a UPC-A the 12th, and on an ISBN-10 or ISSN the 10th or 8th, where it can be the letter X.

How do I check a whole list of barcodes?

Choose Bulk list, paste one number per line and press Run the list. Each line is marked valid or invalid, with the right check digit when it is wrong. Press Download CSV to save the results, or Copy the results to paste them into a spreadsheet.

Is a GTIN-14 the same as an ITF-14?

GTIN-14 is the 14-digit number; ITF-14 is a barcode often used to print it on cartons. The check digit is the same either way. To draw the ITF-14 barcode, use the Barcode Generator.

My number is valid here. Does that mean it is registered?

No. The check digit only shows the digits agree with each other. Whether a GTIN belongs to a company, or an ISBN to a publisher, is recorded by GS1 member organisations and ISBN agencies, not in the number itself.

Is anything I type sent to a server?

No. The sums run in your browser, and the CSV is made on your device. You can check: open your browser's developer tools, go to the Network tab, and use the tool. The page counts visits and copies or downloads (tool name only) with analytics that sets no cookies, and never sends the numbers you type (see privacy).