Percent Error Calculator
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Calculate percent error between a measured and actual value. Shows absolute error, direction, and relative error.
Enter your values below and click Calculate for instant results.
Percent error measures how far off an experimental or measured value is from the accepted or theoretical value, expressed as a percentage of the true value. It is a standard tool in science labs, engineering, and any field where measurements are compared against known standards or expected values.
A low percent error does not always mean a measurement is accurate in an absolute sense. A 2% error measuring something very small might be meaningless, while a 2% error on a very large measurement could be significant. Always consider percent error in the context of the actual values and the precision required by the application.
Percent error equals the absolute difference between the measured and actual values, divided by the actual value, multiplied by 100. The absolute value is used because the direction of the error (over or under) is usually reported separately. A positive error means the measured value was higher than the actual value; a negative error means it was lower.
What counts as an acceptable percent error depends entirely on the application. In a high school chemistry experiment, errors under 5% are generally considered reasonable. In pharmaceutical manufacturing, tolerances might be as tight as 0.1%. In everyday measurement for cooking or construction, errors of 2 to 5% are usually acceptable.