# How Do I Calculate Percent Deviation?

In statistics and many other fields of science, the term “percent deviation” is used to describe how far from the truth test results might be. To figure out the percent deviation, you need a calculator and a way to compare your data to a standard.

## Compare your information to the norm.

In many experiments and activities where you record data, you are given a standard or a theoretical result to look for in your data. For example, in a physics lab that figures out how fast something is falling, the acceleration due to gravity is known to be 9.8 m/s2. Your calculated result might not be exactly 9.8 m/s2 because of small mistakes in measuring distance or time to fall. Check how close your result is to the standard after you’ve done your experiment and your math.

## See what’s different.

Find the difference between your answer and the standard by taking the smaller number and dividing it by the bigger number. For example, if you found 9.5 m/s2, the difference would be 9.8 m/s2 – 9.5 m/s2 = 0.3 m/s2.

## Find the percent difference

The percent deviation is calculated by multiplying the difference between your data and the standard by 100 and then dividing that number by the standard. 100 * (data – standard) / (standard) For the acceleration experiment, the formula is: 100 * (9.8 – 9.5)/(9.8) = 100 * (0.3)/(9.8) = 3.06%