Percent Error Calculator
Compare a measured value to the true value as a percentage.
Enter your experimental (measured) value and the actual (true or accepted) value to find the percent error — how far off a measurement is, as a percentage of the true value. Common in science labs and quality checks.
Percent error is always reported as a positive number, since it measures the size of the deviation regardless of direction.
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Formula
Percent error
(|measured − actual| ÷ |actual|) × 100
Example: measured 98 vs actual 100 → (|98 − 100| ÷ 100) × 100 = 2%.
How to use the percent error calculator
- 1Enter the experimental (measured) value.
- 2Enter the actual (true / accepted) value.
- 3Read the percent error; copy or share it.
Examples
| Example | Input | Result |
|---|---|---|
| Slightly low | measured 98, actual 100 | 2% |
| Exact | measured 100, actual 100 | 0% |
| Lab value | 9.8 vs 9.81 | ≈ 0.1% |
How to calculate percent error
Subtract the actual value from the measured value, take the absolute value, divide by the absolute value of the actual value, and multiply by 100. The absolute values make the result positive — percent error describes the magnitude of the error, not its sign. A measured 9.8 m/s² against the accepted 9.81 m/s² is (|9.8 − 9.81| ÷ 9.81) × 100 ≈ 0.1%.
Percent error vs. percent difference
Percent error compares a measurement to a known, accepted true value (it divides by that true value). Percent difference compares two values when neither is more 'correct' than the other (it divides by their average). Use percent error in experiments with a reference value; use percent difference to compare two independent measurements.
Frequently asked questions
What is the percent error formula?
Percent error = (|measured − actual| ÷ |actual|) × 100. The result is the size of the error as a percentage of the true value.
Can percent error be negative?
By convention, no — the absolute value makes it positive, since it measures how far off a value is, not the direction.
What is a good percent error?
It depends on the field. In many lab settings under 5% is considered good, but precision requirements vary widely.
How is it different from percent difference?
Percent error compares to a known true value; percent difference compares two values with no reference, dividing by their average.
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