About the percent error calculator
Percent error tells you how far a measured or estimated value is from the true or accepted value, as a percentage of the true value. This calculator gives the percent error, the absolute error and the signed direction (high or low).
It is widely used in science labs, quality control and engineering to judge the accuracy of a measurement.
Who should use the percent error calculator
- Students writing lab reports.
- Technicians checking instrument accuracy.
- Anyone comparing a forecast or estimate with an actual value.
How to use the percent error calculator: what each input means
- Observed value
- What you measured or estimated.
- True value
- The accepted or actual value. It cannot be zero.
How the percent error calculator works: method and formula
The absolute error is the size of the difference between observed and true values. Percent error divides that difference by the true value and multiplies by 100. The signed version keeps the direction so you can see whether you were above or below.
- Percent error
- % error = |observed − true| ÷ |true| × 100
- Absolute error
- |observed − true|
How to read your percent error calculator result
Smaller is better. A percent error of 1% means the measurement was within a hundredth of the true value. Compare it with the tolerance expected for your instrument or experiment.
Percent error needs a trustworthy true value. If you are comparing two experimental values with no accepted standard, use percentage difference instead.
Percent Error Calculator worked example
A measurement of 56.891 compared with a true value of 62.327.
- Absolute error = |56.891 − 62.327| = 5.436.
- Percent error = 5.436 ÷ 62.327 × 100 = 8.7217%.
- Because the observed value is lower than the true value, the signed error is negative.
Percent error ≈ 8.72%.
Practical uses of the percent error calculator
- Reporting experimental accuracy in a lab write-up.
- Checking a measuring device against a reference standard.
- Comparing a forecast with the outcome.
Assumptions and limitations of this calculator
- The true value must be non-zero; otherwise percent error is undefined.
- Percent error says nothing about uncertainty or repeatability. A single measurement can be accurate by luck.