Percent Error Calculator
Measure how far an experimental or estimated value strays from the true value, as the percentage every lab report asks for.
Percent error
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Absolute error —
Signed error —
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How it works
Percent error = |measured − true| ÷ |true| × 100Frequently Asked Questions
How do I calculate percent error?
Take the absolute difference between your measured and the accepted value, divide by the accepted value, multiply by 100. Measuring 9.6 m/s² against the true 9.81 gives (0.21/9.81)×100 ≈ 2.14%.
Can percent error be negative?
The standard convention uses absolute values, so no — though some fields keep the sign to show direction (over- vs under-estimate). This calculator shows both.
What is an acceptable percent error?
Context decides: under 5% is typical for school labs, under 1% for careful instrumentation, parts-per-million for metrology.