Percent Error Calculator
Calculate the percent error between an observed (measured) value and a true (accepted) value. Useful for lab reports, measurement accuracy checks, and forecast-vs-actual comparisons.
Your Result
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| Result | What it means? |
|---|---|
| < 1% | Excellent Errors below 1% indicate very high measurement accuracy. |
| 1 – 5% | Good Errors between 1% and 5% are typical for many scientific measurements. |
| 5 – 10% | Acceptable Errors between 5% and 10% are reasonable for rough estimates and field measurements. |
| 10 – 25% | Poor Errors between 10% and 25% suggest a noticeable discrepancy worth investigating. |
| ≥ 25% | Very poor Errors of 25% or more indicate a significant mismatch between observed and true values. |
| — | No result Inputs are out of range or the true value is zero. |
Percent Error Formula
Percent Error = |observed − true| / |true|
Percent error is the absolute difference between observed and true values, divided by the absolute true value, expressed as a percentage.
- Absolute values are used in both numerator and denominator, so the result is always non-negative regardless of the sign of the difference.
- The percent error scales with the size of the true value — small true values can produce large relative errors even when the absolute difference is small.
This calculator performs straightforward percent-error arithmetic. It does not store or transmit your inputs — every calculation runs entirely in your browser.