Percent Error Calculator
Compare an experimental value to a theoretical (accepted) value and get percent error, absolute error, and relative error. Toggle signed mode to keep direction.
Enter your values
Percent error
1.0204%
Experimental is below the theoretical value.
- Absolute error
- 0.1
- Relative error
- 0.010204
Frequently Asked Questions about the Percent Error Calculator
What is the formula for percent error?
Percent error equals the absolute difference between experimental and theoretical values, divided by the absolute theoretical value, times 100. In symbols: |experimental - theoretical| / |theoretical| * 100. The result is always non-negative.
When do I use percent error in a lab?
Any time you measure a quantity with a known accepted value: density of water, boiling point of a solvent, gravitational constant in a pendulum experiment. It tells you how close your measurement got to the textbook value.
What is the difference between signed and absolute percent error?
Absolute drops the sign and only reports magnitude (standard for most lab reports). Signed keeps the sign so you can see whether your measurement was above (+) or below (-) the accepted value.
What does direction over or under mean?
Over means your experimental value is greater than the theoretical, under means less, exact means they match. Useful even in absolute mode because it tells you which way your systematic error leans.
Why can't the theoretical value be zero?
Percent error divides by the theoretical value, so a zero denominator is mathematically undefined. If your reference value is zero, report the absolute error in raw units instead of a percentage.