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How to Calculate Percent Error

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Direct answer

Subtract the reference from the measured value, take the absolute value, divide by the absolute reference value, and multiply by 100.

Formula and method

|measured−reference|/|reference| × 100

This page must show the formula exactly as the calculator or worked method uses it. Inputs remain unrounded during the calculation; rounding applies only to the displayed answer unless a domain-specific rule requires otherwise.

Step-by-step calculation

  1. Identify the reference value rather than assuming the first number is correct.
  2. Find the signed error measured−reference.
  3. Take its magnitude for absolute percent error.
  4. Divide by |reference| and multiply by 100.

Worked examples

Chemistry

9.82 g measured versus 10.00 g reference: 0.18 ÷ 10.00 × 100 = 1.8%.

Timing

2.04 s measured versus 2.00 s reference: 0.04 ÷ 2.00 × 100 = 2%.

Temperature

98.1 versus 100.0: 1.9% absolute error; signed error −1.9%.

Interpretation and edge cases

  • Keep units identical.
  • Do not round the difference before division.
  • If the reference is an estimate with uncertainty, report that context.

Frequently asked questions

Which number is on the bottom?

The absolute reference value.

Why take the absolute value?

It reports error magnitude independent of direction.

Should I show the sign?

Show it separately as signed relative error when direction matters.

Sources and transparency

The formulas and examples were evidence-checked on 2026-09-10. This is educational mathematical content. It does not replace a field-specific standard, accounting policy, laboratory method, contractual definition or professional judgment. CalculatorGeek should display a named human reviewer only after a real reviewer has completed and documented that review.

Keep exploring

4 available tools
Signed vs Absolute Percent ErrorUnderstand why absolute percent error is nonnegative while signed relative error shows high or low bias.Absolute Error vs Relative Error vs Percent ErrorCompare absolute error, relative error and percent error with formulas, units and worked examples.Percent Error vs Percentage DifferenceUse percent error when one value is a reference and percentage difference when two values are peers. Compare formulas and examples.Percent Error With Zero or Near-Zero Reference ValuesUnderstand why percent error is undefined at a zero reference and unstable near zero, plus safer reporting alternatives.