What is percent error?

Percent error = (|Experimental − Accepted| / |Accepted|) × 100. It quantifies the accuracy of a measurement relative to the true value.

What is a good percent error?

Under 5% is typically acceptable in most lab contexts. Under 1% is excellent. Above 10% suggests a systematic error or incorrect method.

Is percent error the same as percent difference?

No. Percent error compares one measurement to a known standard. Percent difference compares two measurements with neither considered the reference.

Percent Error Calculator

Enter your experimental (measured) value and the accepted (theoretical or known) value to compute percent error, absolute error, relative error, and an accuracy rating.

How to use this calculator

Enter your experimentally measured value.
Enter the accepted or theoretical value (e.g. from a textbook or standard).
Read percent error, absolute error, and an accuracy rating.

Formula & method

Percent error formula

% Error = (|Experimental − Accepted| / |Accepted|) × 100

The absolute value ensures percent error is always positive. Some conventions retain the sign to indicate direction.

Example

Experimental = 9.8 m/s², Accepted = 9.80665 m/s² → |9.8 − 9.80665| / 9.80665 × 100 ≈ 0.068%.

Key insights

Percent error < 1% is generally considered excellent in a school or undergraduate lab setting.
Percent error is always expressed as a percentage of the accepted value, not the experimental value.
Sources of error include instrument precision, parallax, systematic bias, and sample contamination.
A positive percent error means your measurement overestimated the true value; negative means underestimated.

How to interpret your result

Accuracy vs precision

Accuracy is closeness to the true value (low percent error). Precision is consistency across repeated measurements, which this calculator does not assess.

Direction of error

If experimental > accepted, the measurement overestimates the true value. If experimental < accepted, it underestimates.

Frequently asked questions

What is percent error?: Percent error = (|Experimental − Accepted| / |Accepted|) × 100. It quantifies the accuracy of a measurement relative to the true value.
What is a good percent error?: Under 5% is typically acceptable in most lab contexts. Under 1% is excellent. Above 10% suggests a systematic error or incorrect method.
Is percent error the same as percent difference?: No. Percent error compares one measurement to a known standard. Percent difference compares two measurements with neither considered the reference.

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