Measure relative error between experimental results and known reference values.
Overview
Percent error compares a measurement to an accepted reference, scaling absolute difference by the magnitude of the true value. It is standard in chemistry labs, physics experiments, and calibration checks.
The usual formula is |experimental − true| / |true| × 100%. Absolute value prevents negative errors from looking smaller than they are, while dividing by true value makes errors comparable across scales.
Small percent error suggests good agreement; large error triggers investigation of technique, instruments, or assumptions. Always report units and whether true value is a literature constant or instrument standard.
Percent error differs from percent difference when comparing two experimental peers without a gold-standard reference. Pick the formula that matches your rubric or publication guidelines.
Steps
Your measured result.
True, theoretical, or standard reference.
Subtract and take magnitude.
Normalize relative to reference.
Multiply by 100 for percent error.
Compare with lab tolerance or spec sheet.
Math
Percent Error = |Experimental − True| / |True| × 100%
Absolute deviation scaled by reference magnitude expresses relative accuracy as a percentage.
Worked cases
|19.2−20|/20 × 100 = 4%
4% error.
0.02/10 × 100
0.2% error.
5/10 × 100
50% error.
Why use this
Questions