Percent Error Calculator

Enter the value you measured and the accepted or theoretical value to see the unsigned percent error.

How it works

Percent error asks how far a measurement sits from a known reference, relative to that reference. The difference is taken in absolute value, so measuring 9 or 11 against 10 both give 10%.

Dividing by the theoretical value — not the experimental one — is what makes the figure a relative error. When the accepted value is 0 the formula is undefined, and the tool does not invent a percentage.

Formula

Percent error = |experimental − theoretical| ÷ |theoretical| × 100

Worked examples

A lab density
experimental 1.25, theoretical 1.20 → 4.1667%
Either side of 10
9 vs 10, or 11 vs 10 → 10%

Useful notes

This is not percentage change (old vs new) and not a plain percentage of a number.
The result is unsigned. Sign would be a signed relative error, which this page does not report.

FAQ

What is the percent error formula?: Take the absolute difference between the experimental and theoretical values, divide by the absolute theoretical value, and multiply by 100.
Can percent error be more than 100%?: Yes. If you measure 3 against an accepted 1, the error is 200%. The figure is a relative gap, not a score that stops at 100.
Why is a theoretical value of 0 rejected?: You cannot divide by zero. There is no finite percent error against an accepted value of 0.

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