Percent Error Calculator
Calculate the percentage error between an estimated and exact value
About this calculator
Percent error measures how far off an estimate or measurement is from the true value, expressed as a percentage of the true value. Formula: |Estimated − Exact| / |Exact| × 100. A lower percent error means higher accuracy. This is widely used in science experiments, quality control, and forecasting.
How to use
Estimate: 9.8, True value: 10. Percent error = |9.8 − 10| / 10 × 100 = 2%. Your estimate was 2% off from the true value.
Frequently asked questions
Is percent error always positive?
Yes, because we use absolute value in the formula. Percent error measures magnitude of error, not direction. If you need to know whether you overestimated or underestimated, look at the raw difference (estimated minus exact).
What is an acceptable percent error?
It depends on the context. In many science experiments, below 5% is considered acceptable. In engineering or manufacturing, tolerances may be much tighter — sometimes below 0.1%.