Percent Error Calculator
Calculate percent error, absolute error and relative error between a measured value and the true value.
Percent error
5%
Absolute error
0.5
Relative error
0.05
Percent error = |measured \u2212 true| / |true| \u00D7 100. It tells you how close a measurement is to the accepted value.
Last updated: February 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Percent error is the standard way to express measurement accuracy, and this calculator makes it instant for students and professionals. In Indian schools, physics and chemistry labs require students to compare experimental results with accepted textbook values and report the percent error in their practical files. Quality control engineers use it to check whether manufactured parts stay within tolerance, such as verifying that a resistor or packaged product matches its specification. Pharmacists and medical labs validate instrument readings against known standards using the same calculation. Meteorologists compare forecasted temperatures with actual readings to judge model accuracy. The calculator shows absolute error, relative error and percent error together, so a single entry gives the complete picture of how far a measurement deviates from the accepted value.
How to Use This Calculator
- Step 1: Enter the measured value from your experiment, such as 9.5.
- Step 2: Enter the true or accepted value, such as 10.
- Step 3: Read the percent error, absolute error and relative error in the results.
- Step 4: Compare the percent error with your lab's tolerance to judge how accurate the measurement is.
Worked Example
A Class 11 student in Delhi measures the density of water in the lab and gets 9.5 units against the textbook value of 10 units. She enters 9.5 as the measured value and 10 as the true value. The calculator reports an absolute error of 0.5, a relative error of 0.05 and a percent error of 5%, well within her lab's 10% acceptance limit. Her friend measures a resistor as 25 ohms against a labelled value of 20 ohms, giving a percent error of 25%, far beyond tolerance, so the friend rechecks the multimeter. When a measurement exactly matches the true value, the error is 0%.
Tips and Common Mistakes
- •Tip 1: Percent error is always positive, since it uses absolute values to show the size of the mistake, not its direction.
- •Tip 2: In experiments, a percent error under 5% is generally considered precise, but always follow your teacher's or company's tolerance.
- •Tip 3: Recalculate after correcting a procedural mistake, because systematic errors often inflate the same result repeatedly.
- ✗Mistake 1: Using a true value of zero, which makes the percentage undefined because division by zero has no meaning.
- ✗Mistake 2: Confusing percent error with percentage change: percent error compares with a known true value, while percentage change compares two measurements over time.
Frequently Asked Questions
What is percent error?
Percent error measures how far a measured value is from the accepted true value, expressed as a percentage of the true value. It is always reported as a positive number.
How is percent error calculated?
Take the absolute difference between the measured and true values, divide by the absolute true value, and multiply by 100. For example, measuring 9.5 against a true 10 gives 5% error.
What is the difference between absolute and relative error?
Absolute error is the raw difference, like 0.5. Relative error expresses that difference as a fraction of the true value, such as 0.05, and percent error is relative error times 100.
Where is percent error used?
Physics and chemistry lab experiments compare measured results with textbook values. It is also used in quality control, manufacturing tolerance checks and instrument calibration.
What if my measured value equals the true value?
Then the percent error is exactly 0%, meaning the measurement is perfect. In practice, small errors are normal due to equipment limits and reading precision.
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