# 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.

1. ### Compare your data to the standard

In many experiments or data-recording 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.

2. ### 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.

3. ### 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%