How to Calculate Experimental Error in Chemistry

Error is a measure of accuracy of the values in your experiment. It is important to be able to calculate experimental error, but there is more than one way to calculate and express it. Here are the most common ways to calculate experimental error:

Error Formula

In general, error is the difference between an accepted or theoretical value and an experimental value.

Error = Experimental Value - Known Value

Relative Error Formula

Relative Error = Error / Known Value

Percent Error Formula

% Error = Relative Error x 100%

Example Error Calculations

Let's say a researcher measures the mass of a sample to be 5.51 grams. The actual mass of the sample is known to be 5.80 grams. Calculate the error of the measurement.

Experimental Value = 5.51 grams
Known Value = 5.80 grams

Error = Experimental Value - Known Value
Error = 5.51 g - 5.80 grams
Error = - 0.29 grams

Relative Error = Error / Known Value
Relative Error = - 0.29 g / 5.80 grams
Relative Error = - 0.050

% Error = Relative Error x 100%
% Error = - 0.050 x 100%
% Error = - 5.0%