Quick answer
Percent error = |measured − true| ÷ |true| × 100. A measurement of 48 against a true value of 50 has an error of 2 ÷ 50 = 4%.
Enter the measured value and the accepted (true) value. The calculator returns the percent error.
Related tools: Percent Off Calculator: Find the sale price and savings after a percentage discount. Decimal to Percent Calculator: Convert a decimal to a percentage. Percent Increase Calculator: Percentage increase between two values.
How to use the Percent Error Calculator
- Enter measured value.
- Enter true (accepted) value.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Measured value | A number | — |
| True (accepted) value | A number | — |
Formula and method
Formula
percent error = |measured − true| ÷ |true| × 100
IEEE-754 double precision; shown to at most 6 decimal places.
Absolute error relative to the accepted value.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Measured value = 48; True (accepted) value = 50.
| Result | Value |
|---|---|
| Percent error | 4 % |
Example 2
Inputs: Measured value = 52.5; True (accepted) value = 50.
| Result | Value |
|---|---|
| Percent error | 5 % |
The first line is the headline result (percent error). IEEE-754 double precision; shown to at most 6 decimal places.
Absolute and signed error
The page reports the size of the error, using the absolute difference. Some textbooks keep the sign to show whether the measurement was too high or low: (48 − 50) ÷ 50 = −4%, meaning 4% low.
Where this estimate stops applying
The true value cannot be 0, since dividing by zero is undefined. Percent error compares an experimental result with a known value; for comparing two experimental values, percent difference is used instead.
How the result changes with measured value
Holding every other input at the first worked example, this table changes only measured value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Measured value | Percent error |
|---|---|
| 24 | 52 % |
| 48 | 4 % |
| 96 | 92 % |
| 192 | 284 % |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- True (accepted) value: entering "0" shows "The true value must not be 0." beside that field and no result.
Choosing between the Percent Error Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Percent Off Calculator](/math/percent-off-calculator/) | original price and discount | Sale price |
| [Decimal to Percent Calculator](/math/decimal-to-percent-calculator/) | decimal | Percent |
| [Percent Increase Calculator](/math/percent-increase-calculator/) | original value and new value | Percentage increase |
| [Percent to Fraction Calculator](/math/percent-to-fraction-calculator/) | percent | Fraction |
| [Percent to Ratio Calculator](/math/percent-to-ratio-calculator/) | percent | Ratio |
Background: rounding and basic arithmetic
Rounding to a place looks at the digit just to its right: 0 to 4 rounds down and 5 to 9 rounds up (the half-up convention, so 2.5 becomes 3). Rounding 838.274 gives 800 to the nearest hundred, 840 to the nearest ten and 838 to the nearest one.
Some systems use banker's rounding (half to even), which sends 2.5 to 2 and 3.5 to 4; check which convention your task requires, and round only at the end of a multi-step calculation.
Assumptions and limitations
- True value 0 is undefined
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for true (accepted) value to confirm this.
Frequently asked questions
What is a good percent error?
It depends on the experiment; many labs aim for under 5%.
Is percent error the same as percent difference?
No, percent difference compares two measured values.
Can percent error exceed 100?
Yes, if the measurement is more than double or negative.
What does the Percent Error Calculator calculate?
Compare a measured value with the true value. It returns Percent error.
What formula does the Percent Error Calculator use?
percent error = |measured − true| ÷ |true| × 100. Absolute error relative to the accepted value.
What do I need to enter in the percent Error Calculator?
You enter Measured value and True (accepted) value.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. True value 0 is undefined.
What is an example of a percent Error result?
With measured value 48 and true (accepted) value 50, the percent error is 4 %.
Related calculators
- Percent Off Calculator — Find the sale price and savings after a percentage discount.
- Decimal to Percent Calculator — Convert a decimal to a percentage.
- Percent Increase Calculator — Percentage increase between two values.
- Percent to Fraction Calculator — Convert a percentage to a simplified fraction.
- Percent to Ratio Calculator — Express a percentage as a part-to-whole ratio.
- Percent Decrease Calculator — Percentage decrease between two values.
Sources
- OpenStax, Prealgebra 2e (Rice University): fractions, decimals, percents, ratios and rounding
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.