Percent Error Calculator
Compare a measured value against the true value as a percentage.
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Step by step
The formula
percent error = |measured − actual| ÷ |actual| × 100
Percent error expresses how far a measurement sits from the accepted value, relative to that value. Dividing by the true value rather than the measurement is what makes errors comparable across experiments of completely different scales.
All calculations run locally in your browser and update instantly as you type.
Example calculations
Common questions this calculator answers — select one to load its values.
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Frequently asked questions
Should percent error be negative?+
The standard definition uses the absolute value, so it is never negative. This tool reports the size separately from the direction so you keep both pieces of information.
What counts as a good percent error?+
It depends entirely on the field. School experiments often accept under 5%; precision engineering may require under 0.1%. Compare against the tolerance for your context, not a universal figure.
All calculations run locally in your browser. Nothing you type is sent to a server.