Percent Error Calculator

1. Enter the experimental value. This is the value you measured or observed in your experiment. For example, you measured 9.8 m/s² for gravitational acceleration.
2. Enter the theoretical value. This is the accepted or true value from a reference. For gravitational acceleration, the accepted value is 9.81 m/s² (or 10.0 in simplified problems).
3. Read the results. Percent error tells you how far off your measurement was as a percentage of the true value. Absolute error is the raw difference. Relative error is the fraction form.

Percent error is always expressed as a positive number. The formula uses absolute value so it does not matter whether your measurement was too high or too low.

Percent Error = |Experimental - Theoretical| / |Theoretical| × 100

Where:
  Experimental = your measured value
  Theoretical  = the accepted or true value

Example:
  Experimental = 9.8, Theoretical = 10.0
  Absolute Error   = |9.8 - 10.0| = 0.2
  Relative Error   = 0.2 / 10.0   = 0.02
  Percent Error    = 0.02 × 100   = 2%

Another example (measuring 10.3 when truth is 10.0):
  Absolute Error   = |10.3 - 10.0| = 0.3
  Percent Error    = 0.3 / 10.0 × 100 = 3%