Percentage Error Calculator
Compares a measured or experimental value against the accepted/theoretical value — the standard calculation for lab reports.
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How to calculate percentage error
- Type the accepted or theoretical value.
- Type your measured (experimental) value.
- Read the percentage error, ready for your lab report.
The formula
% error = (|experimental − theoretical| ÷ |theoretical|) × 100
The absolute value means percentage error is always reported as positive — it measures the size of the discrepancy, not its direction. Commonly used in physics and chemistry lab work to express how far a measured result strayed from the expected value.
Questions about percentage error
What is the percentage error formula?
Percentage error = |measured − accepted| ÷ |accepted| × 100. If you measure gravity as 9.6 m/s² and the accepted value is 9.81, the error is 0.21 ÷ 9.81 × 100 ≈ 2.14%.
Is percentage error always positive?
Yes, as it is usually reported. It uses the absolute difference, so it shows how far off the result was, not in which direction.
What counts as a good percentage error?
It depends on the experiment and equipment. In school science, under about 5% is often considered good, but your teacher or method may set a different limit.
What is the difference between percentage error and percentage difference?
Percentage error compares a result with a known correct value. Percentage difference compares two values when neither one is known to be correct.