What is percent error?
Percent error measures the difference between an approximate value and an exact value as a percentage of the exact value.
Percent Error Calculator
Measure how far an approximate or experimental value is from the accepted exact value.
Enter approximate and exact values
Provide the measured/approximate value and the true/exact value.
About this calculator
How to use Percent Error Calculator, plus the formulas and logic behind the results.
Tool description
Percent error compares an approximate result with a known exact value using absolute differences, so the result is always non-negative.
How to use
- Enter the approximate or experimental value.
- Enter the exact or accepted value.
- Select Calculate to view percent error.
- Review the absolute difference for context.
Formulas & reference
Percent error = |approximate − exact| ÷ |exact| × 100
Lab tips
- Lower percent error means closer agreement
- Always use the accepted true value as “exact”
- Report units consistently on both inputs
- Exact = 0 is not allowed in this formula
Calculation logic
The absolute difference is divided by the absolute exact value and scaled by 100. An exact value of zero is rejected.
Percent error is unsigned. Use percent change if you need direction (overestimate vs underestimate).
Percent Error Calculator FAQ
Common questions about this calculator and how to use the results.
Is percent error always positive?
Yes. Absolute values remove the sign so the result shows magnitude only.
What if my exact value is zero?
The standard formula divides by the exact value, so zero is not allowed.
How is this different from percent difference?
Percent error compares against a known true value; percent difference treats both values symmetrically.
Can approximate be larger than exact?
Yes. Absolute value means overestimates and underestimates produce the same percent error.
When is percent error used?
It is common in science labs, measurement checks, and approximation quality reviews.