Percent error calculator

How far is a measurement from the accepted value, as a percentage of that value?

Formula Percentages

Percent error

Rounded for display

Signed error: ≈ -2.1407%
Absolute error: 0.21

How it works

Percent error compares an experimental or estimated value with a known, accepted value. Subtract one from the other, ignore the sign, divide by the accepted value and multiply by 100.

The signed error keeps the sign: negative means the measurement was too low, positive means too high.

Formula

Percent error = |measured − actual| ÷ |actual| × 100
Signed error = (measured − actual) ÷ |actual| × 100

Worked example

A pendulum experiment gives g = 9.6 m/s² against the accepted 9.81 m/s². The error is |9.6 − 9.81| = 0.21, and 0.21 ÷ 9.81 × 100 ≈ 2.14%. The signed error is −2.14%: the measurement was low.

Questions people ask

Can percent error be negative?

The usual definition uses the absolute value, so it is never negative. The signed version shows whether you were over or under.

What counts as a good percent error?

It depends on the field and the instruments. School experiments often accept a few percent; precision engineering may require far less.