Percent Error Calculator
Adjust the inputs below. Results update as you type.
How it works
Percent error = |measured − actual| / |actual| × 100%. The absolute value makes it non-negative by default; signed error shows direction. Used in physics and chemistry labs to assess measurement accuracy. Systematic error (consistent offset) differs from random error (scatter)—percent error captures both. A value above 5% typically warrants rechecking the experimental method.
Input guidance
- Check units and decimal placement before running calculations.
- For percentage and ratio tasks, define the baseline value clearly.
- Use rounded output carefully and keep full precision for intermediate steps.
The formula
Percent error = |experimental − actual| ÷ |actual| × 100. It measures how far a measured value deviates from the true or accepted value.
Worked example
Measuring 9.8 when the true value is 10 gives |9.8 − 10| ÷ 10 × 100 = 2% error.
More examples to test
- Baseline example: solve with clean numbers first to verify formula direction.
- Edge-case example: test near-zero or boundary values to avoid interpretation errors.
How to interpret results
Use outputs as quick checks, then verify with step-by-step work for graded or high-stakes use.
When this can be inaccurate
Errors usually come from unit mismatch, wrong baseline assumptions, or rounding too early in multistep problems.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Build math and logic skills with guided lessons
Educational platform recommendation.
Frequently asked questions
What is percent error?+
The size of the difference between a measured value and the true value, expressed as a percentage of the true value.
Can percent error be negative?+
Typically it uses absolute value, so it is reported as a positive magnitude. Some contexts keep the sign to show direction of the error.
What is a good percent error?+
It depends on the field. Small errors (under a few percent) often indicate good accuracy, but precision requirements vary by experiment.
Why do my classroom and calculator results differ?+
Differences usually come from rounding conventions, order-of-operations handling, or different baseline assumptions.
What is the safest way to validate an answer?+
Recompute with units shown and check against a second method or manual arithmetic for critical problems.