Percent Error Calculator
Enter your experimental and theoretical values to get absolute error, relative error, and percent error — plus a quick read on how good your result is.
Built for chemistry, physics, and any lab work where you need to know how close your measurement landed to the accepted value. Enter what you measured and what theory says it should be, and get the absolute error, relative error, and percent error instantly — along with a plain-English accuracy rating based on how far off you are.
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How to use
- Enter the value you measured or derived in the 'Experimental Value (E)' field.
- Enter the accepted textbook figure or design specification in the 'Theoretical Value (T)' field.
- Absolute error, relative error, and percent error are calculated live and displayed as result cards.
- Read the accuracy feedback — excellent, good, acceptable, or significant deviation — alongside the full formula, and copy whatever you need.
FAQ
- Can percent error come out negative?
- Not here. The standard relative error and percent error formulas take the absolute value of the difference (|E - T|) so the result reflects the size of the error, not its direction. You'll always get zero or a positive number.
- Why can't it calculate when the theoretical value is 0?
- A theoretical value of 0 means there's no denominator to measure a ratio against, so relative and percent error are undefined. Only absolute error is meaningful in that case.
- What's generally considered an "acceptable" percent error in an experiment?
- There's no universal answer, but in typical school chemistry or physics labs, a percent error under 5% is often considered good and under 1% is considered excellent precision. Fields where precision really matters — like instrumentation or engineering design — may demand a much stricter standard, sometimes 0.1% or lower, so what counts as acceptable really depends on the purpose and field of the experiment.