Percent Error Calculator
Percent error calculator: compare a measured value with the true or accepted value, δ = |measured − true| / |true| × 100 %.
δ = |xmeasured − xtrue||xtrue| · 100 %
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Percent error measures how far an experimental result is from the accepted value, relative to that value: δ = |xmeasured − xtrue|/|xtrue| × 100 %.
It is standard in lab reports. A small percent error indicates accuracy, but not necessarily precision: repeat the measurement and use standard deviation for that.
Formula
δ = |xmeasured − xtrue||xtrue| · 100 %
| Symbol | Quantity | Units |
|---|---|---|
| xm | Measured value | — |
| xt | True (accepted) value | — |
| δ | Percent error | %, × |
Worked example
Given: xm = 9.95 · xt = 9.81
δ = |xm − xt||xt|
Result: δ = 1.42712 %
Frequently asked questions
I measured g = 9.95 m/s²; what is my error?
δ = |9.95 − 9.81|/9.81 = 1.43 %.
What is the difference between percent error and percent difference?
Percent error compares with a known true value; percent difference compares two measurements with each other, dividing by their average.