Percent Error Calculator
Percent error between experimental and theoretical values.
Formula
%Err = |Exp − Theo| / |Theo| × 100
How to use
- 1Enter the experimental (measured) value.
- 2Enter the theoretical (accepted) value.
- 3Read the absolute, relative and percent errors.
- 4Note the direction: over- or underestimate.
About this calculator
Every measured value differs a little from the accepted, true one. Percent error tells you how far off you were as a percentage of the correct value, so the same absolute gap reads as a small error on a large quantity but a large error on a tiny one. This calculator returns percent error along with absolute and relative error and whether you over or underestimated.
Formula explained
Absolute Error = |Experimental − Theoretical|. Relative Error = Absolute Error ÷ |Theoretical|. Percent Error = Relative Error × 100. The direction (over or underestimate) hints at systematic bias in your setup rather than random noise.
Worked example
|9.7 − 9.81| = 0.11; relative 0.11 ÷ 9.81 ≈ 0.0112; percent error ≈ 1.12% (an underestimate). Within about one percent is generally a good measurement.
Tips & notes
- Always divide by the accepted (theoretical) value.
- Take the absolute value so the percent error is positive.
- Report it to a sensible number of significant figures, not a long decimal.