Percent Error Calculator

Percent error = |experimental − theoretical| ÷ |theoretical| × 100. It measures how far your result is from the accepted value, as a percentage of it.

Because error is measured relative to the true value — being off by 1 matters far more when the true value is 2 than when it is 2000.

The sign comes from experimental − theoretical before the absolute value: positive means you overestimated (measured too high), negative means you underestimated (measured too low).

Under 5% is generally considered good for school labs. 5–10% is reasonable and worth a quick check of your method; over 10% usually points to a systematic error.

Percent error compares a measurement to a known true value. Percent difference compares two values to each other, dividing by their average — use it when neither value is the correct one.