Percent Error Calculator
How far your measurement landed from the accepted value, in percent.
The formula
percent error = |measured - true| / |true| × 100
Measuring gravity as 9.95 m/s² against the accepted 9.81: |9.95 - 9.81| / 9.81 × 100 = 1.43%. The true value is the base, never the measurement.
Reading the number
What counts as a good percent error depends on the experiment: under 1% is excellent for a school lab, while 5 to 10% is normal when timing by hand or reading analog scales. The absolute-value bars make percent error unsigned by convention; if the sign matters (consistently overshooting vs. undershooting), report the signed relative error instead.