Find how far a measurement is from the accepted value, as a percentage.
Percent error = |observed − accepted| ÷ |accepted| × 100. Measuring g as 9.5 m/s² when the accepted value is 9.81 gives a percent error of 3.160041%.
Percent error tells you how close a measured or estimated value is to the true one. Enter your observed (experimental) value and the accepted (theoretical) value; the calculator returns the percent error plus the absolute error, relative error and signed error so you can tell whether you measured too high or too low.
A small percent error means an accurate measurement. Teachers usually accept a few percent in school experiments. For general percentages see the Percentage Calculator; for spread in repeated readings use the Standard Deviation Calculator.
The calculator applies the standard method step by step.
| Item | Value |
|---|---|
| Absolute error | 0.31 |
| Signed error (observed − accepted) | -0.31 |
| Relative error | 0.03160041 |
| Signed percent error | −3.160041% |
| Result | Measured value is below the accepted value |
| Observed value | Percent error |
|---|---|
| Observed 9.0 | 8.256881% |
| Observed 9.5 | 3.160041% |
| Observed 9.81 | 0% |
| Observed 10.0 | 1.936799% |
| Observed 10.5 | 7.033639% |
A measure of how far an experimental value is from the true value, expressed as a percentage of the true value.
|observed − accepted| ÷ |accepted| × 100.
The standard formula uses the absolute value, so it is always positive. The signed error shows the direction.
Under 5% is generally considered good in school labs; precision work demands far less.
Percent error compares to a known true value; percent difference compares two measurements when neither is known to be correct.
Percent error cannot be calculated because it divides by the accepted value; use the absolute error instead.
It uses the standard method: percent error = |observed − accepted| ÷ |accepted| × 100 The full working and a worked example are shown on this page.
Decimal results use standard double-precision arithmetic (about 15–16 significant digits). Tools that work with whole numbers — big numbers, factors, bases, combinations — use exact integer arithmetic, so no digits are lost.
Yes for checking your work and learning the method. The steps and formula are shown so you can understand the answer, but follow your teacher's rules about calculators in exams.
No. Everything is calculated in your browser and nothing you enter is uploaded or saved.
