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Percent error calculator

Percent error tells you how far a measurement is from the accepted value, expressed as a percentage. Enter both values and get the result instantly.

Percent error

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Absolute error

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Signed error

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Relative error

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About this calculator

Formula

Percent error = |measured − theoretical| / |theoretical| × 100

All variables defined:

  • measured: the value you obtained from an experiment or measurement
  • theoretical: the accepted, true, or expected value
  • Absolute error: |measured − theoretical|
  • Relative error: |measured − theoretical| / |theoretical|

Worked example

Gravitational acceleration experiment:

  • Measured: 9.8 m/s²
  • Theoretical (accepted): 9.81 m/s²
  • Absolute error: |9.8 − 9.81| = 0.01
  • Percent error: 0.01 / 9.81 × 100 ≈ 0.102%

Frequently asked

What is percent error?
Percent error = |measured − theoretical| / |theoretical| × 100. It measures how close a measurement is to the true value, always expressed as a non-negative percentage.
What is the difference between absolute and relative error?
Absolute error is the raw difference |measured − theoretical|. Relative error is that difference divided by the true value (a ratio, not a percentage). Percent error is relative error × 100.
Why is percent error always positive?
By convention, percent error uses the absolute value of the difference so it is always non-negative. The signed error field in this calculator shows whether you measured over or under.
What does it mean when theoretical is zero?
Percent error is undefined when the theoretical value is zero because dividing by zero is not allowed. The calculator shows "undefined" in that case.
How do I share my calculation?
Click "Share with my numbers" to copy a URL that restores your measured and theoretical values.