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Modulo 11 Check Digit Calculator

Calculate or validate the ISBN-10 version of a Modulo 11 check digit.

Example values are filled in. Change them to match your job; results update automatically.

How to use this tool ↓

Your inputs

Replace the example values with your own.

Enter digits without spaces or hyphens. A complete ISBN-10 may end in uppercase X.

Calculated result

Check character2
Complete ISBN-100306406152
0×10 + 3×9 + 0×8 + 6×7 + 4×6 + 0×5 + 6×4 + 1×3 + 5×2 = 130 Check value = (11 − (130 mod 11)) mod 11 = 2
This page implements the ISBN-10 weighting method only. Modulo 11 has other industry-specific variants and is not the GS1 check-digit algorithm.

How to use this calculator

  1. Choose calculation for a nine-digit ISBN body, or validation for a complete ISBN-10.
  2. Enter the number; a complete ISBN-10 may end in X.
  3. Read the result. X represents a check value of 10 and is a valid final character in this scheme.

Other Modulo 11 schemes use different rules. Use this calculator only for ISBN-10.

Formula and method

This implementation multiplies the nine ISBN body digits by weights 10 through 2. The check value makes the complete weighted sum divisible by 11; value 10 is represented by X.

Read the methodology and source notes →

Worked example

For ISBN body 030640615, the weighted sum is 130. The check character is 2, producing ISBN-10 0306406152.

How to interpret the result

Use this page only for the legacy ISBN-10 weighting method. The explicit variant prevents a result from being mistaken for another industry's Modulo 11 rule.

Limitations

Modulo 11 is a family of schemes with different weights and remainder mappings. This calculator is not a generic Modulo 11 implementation and is not a GS1 calculator.

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Usage instructions updated October 19, 2026.
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