The Percent Error Calculator finds the percentage difference between an observed (measured) value and the true (accepted) value.
Percent error = 9.0909%
| Percent error | 9.0909% |
| Signed error | -9.0909% |
| Absolute error | 1 |
Calculation steps:
| Formula | |observed − true| ÷ |true| × 100% |
| Substitute | |10 − 11| ÷ |11| × 100% |
| Result | 9.0909% |
Percent error measures how far a measured or estimated value is from the accepted true value, as a percentage of the true value. It is widely used in science labs, engineering and quality control to judge the accuracy of measurements.
Percent error = |observed − true| ÷ |true| × 100%. The absolute value makes the result positive; some fields keep the sign to show whether the measurement was too high or too low.
Worked example (defaults): observed 10, true 11. |10 − 11| ÷ 11 × 100% = 9.0909%. The signed error is −9.09%, meaning the measurement was low.
Percent error compares a value with a known standard. Percent difference compares two measurements when neither is "true", using their average as the base: |a − b| ÷ ((a + b)/2) × 100%.
Use calibrated instruments, repeat measurements and average them, control conditions such as temperature, and read scales at eye level. Systematic errors push results the same way every time; random errors scatter them.
What is an acceptable percent error? It depends on the field; under 5% is often fine in school labs.
Can percent error exceed 100%? Yes, if the observed value is more than double or negative.
Why can't the true value be zero? Division by zero is undefined.