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Percent Error Calculator

The percent error calculator finds the relative error between the observed and true values.

Clear
Percent error1.121305%measured too low
Absolute error0.11
Signed relative error-1.121305%
Accuracy98.8787%

The formula

error = |measured − actual| ÷ |actual| × 100

What a percentage is

"Per cent" means "per hundred", so a percentage is just a fraction with 100 on the bottom. 15% is 15/100, which is 0.15 as a decimal. Every percentage calculation is therefore multiplication or division by a decimal — the percent sign is bookkeeping, not a new operation.

The three questions

Almost every percentage problem is one of three:

  • What is P% of N? Multiply: N × P/100
  • A is what percent of B? Divide: A/B × 100
  • A is P% of what? Divide the other way: A ÷ (P/100)

Recognising which one you have is most of the work; the arithmetic is straightforward once you do.