🎯 Percent Error Calculator
Percent error answers a simple question: how far was my measurement from the truth, in percentage terms? Scientists use it to judge experiments, students use it to check lab work.
Enter the value you observed and the true (accepted) value. The error is always measured against the true value — never against your observation.
How to use this calculator
Enter the value you measured and the true or accepted value, then press Calculate to see your percent error.
- Type your measured result into the Observed value field.
- Type the accepted or exact answer into the True value field.
- Press Calculate and read the percent error, shown as the headline result.
- Check the absolute error and the direction line to see how far off you were and whether you overestimated or underestimated.
Frequently asked questions
What is percent error?
Percent error measures how far a measured value sits from the true value, expressed as a percentage of the true value. A small percent error means the measurement was close; a large one means it was far off.
What is the percent error formula?
Subtract the true value from the observed value, take the absolute value, divide by the absolute true value, and multiply by 100. Always divide by the true value, never by your observed value.
What do overestimate and underestimate mean?
If your observed value is higher than the true value, you overestimated; if it is lower, you underestimated. When both match exactly, the error is zero and the direction reads Exact.
Can you show a worked example?
If you measure 48 but the true value is 50, the absolute error is 2, and 2 divided by 50 times 100 gives a 4 percent error, an underestimate.