Percent Error Calculator
Enter an experimental (measured) value and the true (accepted) value to calculate percent error — a common measure in science and lab work for how far a measurement deviates from the expected result.
How the Percent Error formula works
The percent error formula:
Percent error = |Experimental value − True value| / |True value| × 100
Step-by-step calculation
- Subtract the true value from the experimental value.
- Take the absolute value of that difference, so the result is always positive.
- Divide by the absolute value of the true value, then multiply by 100.
Worked example
An experiment measures a value of 9.8, where the accepted true value is 9.81: Percent error = |9.8 − 9.81| / 9.81 × 100 ≈ 0.10%, a very small deviation.
Frequently asked questions
Why use absolute value in the formula?
Percent error is meant to express the size of the deviation regardless of direction — whether the measured value was too high or too low — so the absolute value keeps the result positive and focused purely on magnitude.
What's considered an acceptable percent error?
It depends entirely on the field and the precision of the measuring equipment involved — some lab contexts expect well under 1%, while other real-world measurements might reasonably accept 5-10% or more. There's no universal threshold.