Percent Error Calculator

Percent error measures how far a measured or estimated value is from the true or accepted value, as a percentage of the true value. It is widely used in science experiments. This calculator finds the absolute error, divides it by the size of the true value and multiplies by 100, and says whether the measurement was high or low.

Try:

How to use the percent error calculator

  1. Enter your measured (experimental) value.
  2. Enter the true (accepted) value.
  3. Press Calculate to see the percent error.

Formula

Percent error=∣measured−true∣∣true∣×100%\text{Percent error} = \frac{|\text{measured} - \text{true}|}{|\text{true}|} \times 100\%

Worked example: g measured 9.6, true 9.81

  • Measured (experimental) value: 9.6
  • True (accepted) value: 9.81

✓ Answer checked

Percent error=2.140673…%\text{Percent error} = 2.140673\ldots\%
Absolute error
0.210.21
Direction
Measured value is too low
Step-by-step working (2 steps)

  1. Find the error

    Subtract and ignore the sign.

    ∣9.6−9.81∣=0.21|9.6 - 9.81| = 0.21

  2. Divide by the true value and × 100 Percent error

    Compare the error with the true value.

    0.219.81×100=2.140673…%\frac{0.21}{9.81} \times 100 = 2.140673\ldots\%
Formulas used
Percent error=∣measured−true∣∣true∣×100%\text{Percent error} = \frac{|\text{measured} - \text{true}|}{|\text{true}|} \times 100\%
How this was checked
  • ✓ Applying the percent error to the true value gives back the size of the error.

Frequently asked questions

Can percent error be negative?

Usually it is given as a positive number using the absolute value. Some teachers keep the sign to show whether the result was too high or too low.

What is a good percent error?

It depends on the experiment, but under about 5% is often considered good in school science.

Is percent error the same as percentage change?

They use similar maths, but percent error compares with a true value, while percentage change compares with a starting value.

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