Percentage Error Calculator
Last updated: November 14, 2026
Direct answer. Percentage error = (|Measured − Accepted| ÷ |Accepted|) × 100. A measured 9.8 against an accepted 10 is a 2% absolute error. The signed error is −2%, because the measurement is low.
Lab courses, quality checks, and instrument checks in U.S. classrooms and shops often ask how far a measured value sits from an accepted or true value. Percentage error reports that gap as a percent of the accepted value. This calculator gives both the absolute percentage error and the signed error that keeps the direction.
Percentage Error Calculator
Compare a measured value with an accepted or true value. The tool reports both the absolute percentage error and the signed error.
Result
Key takeaways
- Absolute percentage error uses the absolute difference over the absolute accepted value.
- 9.8 versus 10 is a 2% absolute error and a −2% signed error.
- An accepted value of 0 makes the percent undefined; the calculator will not print Infinity.
- Units of the two inputs must match; the result is a percent, not the original unit.
How to use this calculator
- Enter the measured or experimental value.
- Enter the accepted, expected, or true value in the same unit.
- Read the absolute percentage error, the signed percentage error, and the raw difference.
The formula
The difference is Measured − Accepted. Signed percentage error keeps that sign. Absolute percentage error drops the sign. Both divide by the absolute accepted value.
Worked examples
| Measured | Accepted | Difference | Signed error | Absolute error |
|---|---|---|---|---|
| 9.8 | 10 | −0.2 | −2% | 2% |
| 10.2 | 10 | 0.2 | 2% | 2% |
| 10 | 10 | 0 | 0% | 0% |
Difference is −0.2. Signed error is −0.2 ÷ 10 × 100 = −2%. Absolute error is 2%.
A measured 10.2 against 10 is also a 2% absolute error, with a signed error of +2%.
When this is useful in the United States
A high school chemistry lab comparing a titer to a known standard can report the absolute percentage error the rubric asked for, and still see whether the result was high or low.
A machine shop checking a pin diameter against a drawing nominal can use the same formula in inches or millimeters, as long as both inputs share a unit.
If a teacher wants relative error as a decimal rather than a percent, divide the displayed percent by 100.
Common mistakes
- Dividing by the measured value instead of the accepted value. That is a different statistic.
- Dropping the sign when the report asked for a signed error, or keeping the sign when the rubric asked for absolute error.
- Using an accepted value of 0.
Call the accepted value what it really is: a textbook constant, a standard mass, or a drawing dimension. If that “accepted” figure is itself an average of messy data, the percentage error only describes the gap you typed, not a formal uncertainty budget. Significant figures and instrument tolerance are left to your lab procedure; this page does not round to a required number of figures beyond ordinary display rounding. Lab rubrics sometimes ask for percent error, sometimes for percent difference, and sometimes for a relative error as a decimal. Use this page only when the base is an accepted or true value. If you are comparing two experimental trials with no “true” value, the percentage difference calculator is the better fit. Keep the measured and accepted values in the same unit: do not compare 9.8 grams with 0.010 kilograms until you convert. The signed error is helpful when a procedure is consistently high or low; the absolute error is what many grade sheets request. Neither figure is a complete uncertainty analysis. If your lab manual defines percentage error without the absolute-value signs, it is asking for a signed figure; use the signed result on this page. If it asks for absolute error, use the absolute result. Copy the working into a lab notebook so the accepted value you used is on the record. Read the result units carefully before you copy them into a spreadsheet, a syllabus, or a checkout estimate. The calculator shows the working so you can compare each step with a hand calculation. If a result looks off, confirm that every input uses the unit labeled on the field, then use Reset and try the built-in example. This page does not invent official rates, cutoffs, or statistics, and it does not store the numbers you type.
Frequently asked questions
What is the percentage error of 9.8 versus 10?
The absolute percentage error is 2%. The signed error is −2%.
Is percentage error the same as percentage difference?
No. Percentage error compares a measurement with an accepted value and uses that accepted value as the base. Percentage difference compares two peers and often uses their midpoint.
What if the accepted value is 0?
The percent is undefined. The calculator shows an error instead of Infinity.
Where can I read a longer walk-through?
See the site guide on how to calculate percentage error.