Science / Measurement
Percent Error Calculator
Calculate the percent error between a measured and a true value, with the absolute and signed error and the working shown.
Percent Error Calculator: Percent error compares a measurement with the accepted value: |measured − true| ÷ |true| × 100. A measured g of 9.68 m/s² against 9.81 gives 1.33%. The signed error keeps the direction, positive when the measurement is too high. The true value cannot be zero, because the formula divides by it. Runs 100% locally in your browser with zero server file uploads.
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|9.68 − 9.81| ÷ |9.81| × 100 = 1.3252%
Reducing error in experiments
Repeat measurements and average them, read scales at eye level, calibrate instruments against known values, and record measurements with all their significant figures. Systematic errors push every result the same way; random errors scatter results either side of the true value.
For averages and spread across repeated measurements, use the statistics calculator.
Percent error and percent difference
Use percent error when a reference value is known, such as g = 9.81 m/s². When two measurements are compared and neither is the reference, use percent difference: |a − b| ÷ ((a + b) ÷ 2) × 100. For changes over time, use percentage increase or decrease instead.
How to use it
- Enter the value you measured in the experiment.
- Enter the true, accepted, or theoretical value.
- Read the percent error, and whether the measurement is high or low.
Privacy & limitations
The calculation runs in your browser.
Related tools
Frequently asked questions
What is a good percent error?
It depends on the experiment: under 5% is often acceptable in school labs, while precise measurements may need well under 1%.
Is percent error the same as percent difference?
No: percent error compares with a known true value; percent difference compares two measurements with each other, dividing by their average.
Can percent error be negative?
The usual percent error uses the absolute value, so it is never negative; the signed error shows whether you were above or below.
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