Percent Error Calculator

Calculate percent error for a lab report from your measured (experimental) value and the accepted (theoretical) value, along with absolute and relative error, rounded to sensible significant figures.

Percent error
2.96%
Unrounded
2.956167%
Absolute error
−0.29
Relative error
−0.029562

Rounded to 3 significant figures, the fewer of the two inputs. Check whether your lab manual wants a different convention.

Step-by-step working

  1. Find the error (measured − accepted)9.52 − 9.81 = −0.29
  2. Take the absolute value|−0.29| = 0.29
  3. Divide by the accepted value0.29 ÷ 9.81 = 0.02956167
  4. Multiply by 100= 2.956167%

Formula percent error = |measured − accepted| ÷ |accepted| × 100%

Ask the tutor about your result

An AI tutor reads your inputs and results above and explains them in plain English. The numbers come from the calculator; the explanation is AI-written, so check it against your notes.

Worked example

You measure g as 9.52 m/s²; the accepted value is 9.81 m/s². Percent error = |9.52 − 9.81| ÷ 9.81 × 100 = 0.29 ÷ 9.81 × 100 ≈ 2.96%. Both inputs have 3 significant figures, so report 2.96%.

Some teachers want the signed version (−2.96%) to show that the measurement was low. Tick “keep the sign” for that.

Percent error vs percent difference

Percent error compares a measurement with a known true value. Percent difference compares two measurements when neither is known to be correct: |a − b| ÷ ((a + b) ÷ 2) × 100. For the spread of repeated measurements, use the relative standard deviation.

Frequently asked questions

What is a good percent error?

It depends on the experiment. In many high-school labs under 5% is considered good and under 10% acceptable, but precise instruments should do much better.

Can percent error be over 100%?

Yes, if the measurement is more than double the accepted value or has the wrong sign. It usually signals a units or setup mistake.