What is percent error/percent deviation?

1 Answer
Aug 15, 2017


relative error between experimental and true results


Percent error and percent deviation are the same thing. They both measure the relative error when you compare the results you got (the experimental/measured results) and compare them to the true or accepted results.

They determine the accuracy of your results. The smaller your percent error, the better your results are. Usually ± 5% is acceptable in class. If it is higher, you might need to go back through your experiment to see what systematic or random errors were present.

Depending on your teacher/professor, the equation for percent error could be one of two equations. I will list both. Just use the one that your professor wants you to use. Some may want you to use the absolute value to express % error as a positive number only.

% error = #(x_(measured)-x_(true))/x_(true)*100%#

% error = #abs((x_(measured)-x_(true))/x_(true))*100%#