How do I calculate percent error? Enter your numbers above and the result updates instantly. For example: Measured value: 9.5 · True value: 10 → Percent error: 5%.
Is this Percent Error Calculator free? Yes — completely free with no sign-up or paywall. It runs entirely in your browser and keeps working offline; the numbers you enter never leave your device.
How accurate is it? It uses the standard published formula for percent error. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.