Percent Error Calculator
How far a measured value is from the true value, as a percentage.
- Absolute difference0.200000
- Percent error2.00%
Inputs used
- Measured value9.8
- True value10
About this calculator
Percent error compares a measurement to the accepted true value: take the difference, divide by the true value, and express it as a percentage — conventionally as an absolute (positive) number. Measuring 9.8 when the true value is 10 is a percent error of 2%.
It's the standard way to report accuracy in lab work because it puts errors on a common scale: being off by 2 grams matters a lot when the true value is 10 grams (20%) and barely at all when it's 10 kilograms (0.02%).
The true value must not be zero — percent error is undefined there, and comparisons near zero can be misleading even when defined.
Frequently asked questions
What is the formula for percent error?
Percent error is the absolute difference between the measured and true values, divided by the true value, times 100: |measured − true| ÷ |true| × 100. Measuring 9.8 against a true value of 10 gives |9.8 − 10| ÷ 10 = 0.02 = 2%.
Can percent error be negative?
By the standard convention, no — the absolute value makes it a non-negative measure of how far off a measurement is, regardless of direction. If you deliberately keep the sign, a negative result just means the measurement was below the true value.
What is the difference between percent error and percent difference?
Percent error compares a measurement to a known true value, dividing by that true value. Percent difference compares two measurements when neither is the accepted standard, dividing by their average instead.
Why can't the true value be zero?
The formula divides by the true value, and division by zero is undefined. Percent error simply has no meaning when the accepted value is zero, and it becomes unstable for true values very close to zero.
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Results are informational only — not financial, medical or legal advice.