Sometimes in your laboratory work, you will use data to determine an experimental value for a quantity that is already known. To evaluate your results, you may need to use percent error to compare your result to value listed in an appropriate literature source.

Percent Error, is the absolute difference between your value and the literature value is divided by the literature value and the quotient is multiplied by 100%.

 

% Error = ( [ |your value - literature value| ] / literature value ) x 100%

 

For example:

A student determines the atomic mass of Aluminium to be 28.9 g. Table in the book says that the atomic mass of Aluminium is 27.0 g. What is student's percent error ?

% Error = ( [ |28.9 - 27.0| ] / 27.0 ) x 100% = 7.0%

Student's percent error equals 7%.