Percent Error Calculator
Calculate percent error from a theoretical and a measured value for your lab report. If you measured several times, get the mean, standard deviation and standard error too.
When repeated values are given, their mean is used instead of the measured value.
Formula
percent error = |measured − theory| / |theory| × 100. It helps to state whether the measurement came out high or low, which the signed relative error shows. The standard deviation of repeated values is the sample standard deviation (divided by n−1).
Frequently asked questions
What is a good percent error in a lab?
It depends on the experiment and the instruments. In introductory circuit labs, results within a few percent are common because resistors are often ±5% and meters add their own error. Compare your percent error with the part tolerances and meter accuracy rather than a fixed number.
Should percent error be positive or negative?
Percent error is usually reported as a positive magnitude. The signed relative error, also shown here, tells you whether the measurement was higher (+) or lower (−) than theory, which is useful when explaining the cause.