Error is a measure of accuracy of the values in your experiment. It is important to be able to calculate experimental error, but there is more than one way to calculate and express it. Here are the most common ways to calculate experimental error:

## Error Formula

In general, error is the difference between an accepted or theoretical value and an experimental value.

Error = Experimental Value - Known Value

## Relative Error Formula

Relative Error = Error / Known Value

## Percent Error Formula

% Error = Relative Error x 100%

## Example Error Calculations

Let's say a researcher measures the mass of a sample to be 5.51 grams. The actual mass of the sample is known to be 5.80 grams. Calculate the error of the measurement.

Experimental Value = 5.51 grams

Known Value = 5.80 grams

Error = Experimental Value - Known Value

Error = 5.51 g - 5.80 grams

Error = - 0.29 grams

Relative Error = Error / Known Value

Relative Error = - 0.29 g / 5.80 grams

Relative Error = - 0.050

% Error = Relative Error x 100%

% Error = - 0.050 x 100%

% Error = - 5.0%