ISBN stands for International Standard Book Number. ISBN-10 uses 10 characters (0–9 and possibly X), and ISBN-13 uses 13 digits. Both contain a checksum to detect typos.

How do I validate an ISBN-10?

Remove hyphens, ensure you have 10 characters, then compute the checksum: sum(i * digit_i) for i=1..10 must be divisible by 11. The last digit can be X = 10.

Can I convert ISBN-10 to ISBN-13?

Yes. Typically you prepend 978 to the first 9 digits of the ISBN-10, then recompute the ISBN-13 checksum. The tool does this automatically when your ISBN-10 is valid.

ISBN Validator

Validate ISBN-10 and ISBN-13, strip hyphens and spaces, see checksum steps, and convert ISBN-10 → ISBN-13.

1. Enter ISBN

You can paste: 978-0-306-40615-7 or 0-306-40615-2 or even 0306406152.

2. Validation Result

Type detected

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Is valid?

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Normalized ISBN

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3. Conversion

ISBN-10 → ISBN-13 only when valid. ISBN-13 → ISBN-10 only when it starts with 978.

ISBN-10 ➜ ISBN-13

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ISBN-13 ➜ ISBN-10

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4. Checksum Steps

Validate an ISBN to see step-by-step checksum here.

How ISBN validation works

ISBN-10

For ISBN-10, after stripping hyphens, you must have 10 characters. The checksum is:

sum(i × d_i) for i = 1..10 must be divisible by 11

The last digit can be X which means 10.

ISBN-13

For ISBN-13, after stripping hyphens, you must have 13 digits. Multiply digits alternately by 1 and 3, sum them, and the total must be divisible by 10.

checksum = (d1×1 + d2×3 + d3×1 + d4×3 + ... + d12×3 + d13×1) mod 10 = 0

This tool implements exactly these algorithms so you can trust the result.

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

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Formula (extracted text)

sum(i × di) for i = 1..10 must be divisible by 11

Formula (extracted text)

checksum = (d1×1 + d2×3 + d3×1 + d4×3 + ... + d12×3 + d13×1) mod 10 = 0

Variables and units

No variables provided in audit spec.

Sources (authoritative):

NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures
FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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