DIY Cost Tools
Percent Error Calculator
MATH CALCULATOR
Compare a measured result with an accepted value using absolute percentage error.
Use consistent units. All fields are required; absolute input values must not exceed one trillion. An accepted value of zero cannot produce a relative percentage error.
How to use this calculator
Replace the example inputs with your measurements, then select Calculate. Results use the units shown beside each field. Keep extra precision in the inputs and round only when recording the final answer.
Formula and explanation
Percent error = |measured − accepted| ÷ |accepted| × 100
The absolute difference measures the size of the error, while the signed difference shows whether the measurement is above or below the reference.
Worked example
With Measured value = 98, Accepted value = 100, the results are Percent error (%): 2; Signed difference: -2.
Important limitations
An accepted value of zero cannot produce a relative percentage error. A very small reference value can make the percentage unusually large.
Results are estimates based on the entered values. Numeric precision does not eliminate measurement uncertainty.
Frequently asked questions
Is this the same as percent change?
No. Percent change compares a later value with a starting value and normally retains its sign. This tool reports the absolute size of a measurement error.
Can values be negative?
Yes. The reference magnitude is used in the denominator, so negative reference values are supported.
What happens if I leave a field blank?
The tool clears the previous result and asks for valid inputs, so an old answer is not mistaken for a new calculation.
Review notes
Reviewed October 1, 2026. Default calculations were checked independently against the displayed equations. The script validates blank, nonfinite, out-of-range, and formula-specific invalid inputs. Calculations run locally in your browser.