Percent Error Calculator

Compare a measured value with the true value to find percent error.

Percent error

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Absolute error

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Signed error

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Direction

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Ratio to true

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Percent error is measured against the true value. The signed error shows whether the measurement was high or low.

How far off was the measurement?

Percent error turns the gap between a measured value and the true value into a single, comparable figure. Scaling by the true value lets you judge accuracy regardless of the size of the numbers involved.

percent error = |measured − true| ÷ |true| × 100

The signed error keeps the direction — positive if the measurement was too high, negative if too low — which the percentage on its own deliberately hides.

Worked example

Measuring 9.8 when the true value is 10 gives an absolute error of 0.2 and a percent error of 2% — the measurement is 0.2 below the accepted value.

Reading the result

Percent error is the standard way to report accuracy in science labs and quality checks. A small value means your measurement is close to the accepted figure; a large one points to a method, instrument or reading worth revisiting.

Worth remembering

Relative, not absolute. A 1-unit error matters more on a small quantity than a large one.
Keep the sign separately. Knowing you read high or low helps diagnose the cause.
Context sets "good". Acceptable error varies hugely by field.

Frequently asked questions

What is the formula?

Percent error = |measured − true| ÷ |true| × 100. The absolute bars make the result positive; a separate signed error shows whether you were over or under.

Why use the true value as the denominator?

Because percent error expresses the mistake relative to the accepted, correct figure — how big the error is compared with what the answer should have been.

Can percent error exceed 100%?

Yes. If the measurement is more than double the true value, or has the wrong sign relative to it, the percent error can be well above 100%.

What counts as a good result?

It depends on the field and the equipment. In a school lab a few percent is often fine; precision work may demand a fraction of a percent. Context sets the bar.