# Percent Error Calculator

Calculate the percent error of a data set. Enter the true value and observed value to determine the percent error of your experiment or calculation.

Percent error is used to determine the accuracy of an experiment or measurement. In simple terms, it’s the difference of the measured value to the known true value. In this case, the true value must be known to determine the real % error. The formula is usually displayed as follows:

Percent Error = abs(True Value – Measured Value)/ True Value

Where abs stands for the absolute value of the difference between the true and measured values. This causes the percent to always be positive, but it does not have to be. In some cases the absolute value is dropped in order to determine which direction the error occurred in, i.e. either too high or too low.

An example of this being used is in an experiment. Lets say you are performing an experiment on some new rare element that has been tested in a certain way. First, you want to set up your experiment with a control in order to determine it’s accuracy. Because of either science, math, or previous experiments, you know what that controls true value should be. Then you run your test and get an experimental error. Next you calculate the percent error, and then you have a gauge for how accurate your test will be on the unknown material.

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