This free online percent error calculator measures how far an experimental (observed) value is from the theoretical (true) value, expressed as a percentage. It's commonly used in science labs and engineering to check the accuracy of measurements and experiments.
How to Use the Percent Error Calculator
Enter the value you measured or observed in the "Experimental (Observed) Value" field.
Enter the accepted or true value in the "Theoretical (True) Value" field.
Click "Calculate" to see the percent error.
Compare the result to your acceptable error tolerance to judge measurement accuracy.
Frequently Asked Questions
It uses Percent Error = |Observed − Theoretical| / |Theoretical| × 100. For example, if the observed value is 9.8 and the theoretical value is 10, the percent error is |9.8 − 10| / |10| × 100 = 2.00%.
Taking the absolute value of the difference and of the theoretical value keeps the percent error non-negative, so it's always reported as a plain percentage regardless of whether the observed value is higher or lower than expected.
Since the theoretical value is the denominator, a value of zero would make the calculation undefined, so the calculator shows "Theoretical value cannot be zero" instead of a result.
Yes, it's completely free to use with no sign-up required.