How Do I Calculate Percent Deviation?
Percent deviation is a term used in statistics and many branches of science to describe how far from accurate test results might be. To find percent deviation, you need a calculator and a standard in which to compare your data.

Compare your data to the standard
In many experiments or datarecording activities, you are given a standard or a theoretical outcome to expect from your data. For example, in a physics lab that calculates the acceleration of a falling object, it’s known that acceleration due to gravity is 9.8 m/s^2. However, due to small errors in measurements of distance or time to fall, your calculated result might not be exactly 9.8 m/s^2. After you have concluded your experiment and your calculations, see how close your result is to the standard.

Find the difference
Find the difference between your calculation and the standard by subtracting the smaller of the two by the larger. For example, if you found 9.5 m/s^2, the equation for the difference is 9.8m/s^2 – 9.5m/s^2 = 0.3m/s^2.

Calculate the percent deviation
The formula for the percent deviation is 100 times the difference between your data and the standard and then divided by the standard. 100 * (data – standard) / (standard) For the acceleration experiment, the formula is written: 100 * (9.8 – 9.5)/(9.8) = 100 * (0.3)/9.8 = 3.06%