Percent Error Calculator
Calculate percent error between an experimental (measured) value and the true (accepted) value. Shows absolute error and relative error.
Last reviewed by the Radiatus Cloud team
Compare a measured value with the true value to find the percent error.
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Measure accuracy with percent error
Percent error expresses how far a measured or experimental value is from the true, accepted value, as a percentage of the true value. It is calculated as the absolute difference between the measured and true values, divided by the absolute true value, multiplied by one hundred. A small percent error means the measurement is close to correct, while a large one signals a bigger discrepancy.
This calculator reports the absolute error, the percent error, and a signed relative error that shows whether the measurement was too high or too low, which the plain percent error hides because it uses the absolute value.
Where percent error is used
Percent error is a standard tool in science laboratories, where students and researchers compare their experimental results against established constants such as the acceleration due to gravity or the density of a material. Engineers use it to assess instrument accuracy, and quality teams use it to check how closely a product meets its target specification.
The true value must not be zero, because dividing by zero leaves percent error undefined. When the accepted value is genuinely zero, an absolute error is reported instead. All calculation happens locally in your browser.
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Frequently Asked Questions
What is the percent error formula?
Percent error equals the absolute value of measured minus true, divided by the absolute value of true, multiplied by one hundred.
Is percent error always positive?
The standard percent error is positive because it uses absolute values. This tool also shows a signed version so you can see whether the measurement was high or low.
Why can the true value not be zero?
The formula divides by the true value. If that value is zero the division is undefined, so percent error cannot be calculated.
What is the difference from percent difference?
Percent error compares a measurement to a known correct value, while percent difference compares two values when neither is considered the true reference.
What counts as a good percent error?
It depends on the field. Many school experiments aim for under five percent, while precision science may require far smaller errors.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Enter the measured value and the true value to get the percent error.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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