Percent Error Calculator

Compare a measured or estimated value with the true value and get the percent error.

Percent error
2.1407%

The measurement is below the true value.

Measured vs true value
0246810True value — Value: 9.81True valueMeasured — Value: 9.6Measured
Absolute error
0.21
Signed relative error
−2.1407%
Show the working
  1. Absolute error = |measured − true| = |9.6 − 9.81| = 0.21
  2. Relative error = 0.21 ÷ |9.81| = 0.021406728
  3. Percent error = 0.021406728 × 100 = 2.14067%

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Formula

Percent error = |measured − true| ÷ |true| × 100

How it works

Percent error is how science classes grade an experiment: it shows how far your result landed from the accepted value, as a share of that accepted value. If you measured gravity as 9.6 m/s² and the accepted value is 9.81 m/s², you were off by 0.21, which is about 2.14% of 9.81.

The standard formula uses absolute values, so percent error is never negative. If you need to know whether you overshot or undershot, look at the signed relative error, which keeps the minus sign when the measurement is too low.

A small percent error means your result is accurate, but it doesn’t say whether it is precise. Repeating a measurement and checking the spread (for example with a standard deviation) tells you about precision.

Frequently asked questions

What is a good percent error?

It depends on the experiment. In many school labs, under 5% is considered good and under 1% excellent, but precise physics or chemistry measurements may expect far less.

Is percent error the same as percentage change?

The arithmetic is similar, but percent error always compares against a known true value and is usually reported as a positive number. Percentage change compares an old value to a new one and keeps its sign.

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