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Math • Percent Error Calculator

Percent Error Calculator

Calculate percent error between an observed (measured) value and the expected (true) value.

Experimental Error
2.00%
Formula: (|Observed - Accepted| / |Accepted|) × 100%
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Calculation Guide & Reference

Percent Error Mathematics

Percent error calculator computes the percentage difference between an observed (measured) value and the expected (true) value.

Standardized Mathematical Formula
% Error = |Observed − Expected| / |Expected| × 100

Measures how far a measured or experimental value is from the accepted/true value, as a percentage of that true value.

Variables:
Observed:Measured or experimental value
Expected:Accepted, true, or theoretical value
How It Works (Step-by-Step)
  • 1Enter the observed (measured) value and the expected (true) value.
  • 2View the percent error, which is always shown as a positive percentage.
Real-World Numerical Example
Measuring 98 Against an Expected 100

A lab measurement comes out to 98, against an accepted/expected value of 100.

•|98 − 100| = 2.
•2 / 100 × 100 = 2%.
Result: The percent error is 2%.
Calculation Best Practices & Tips
Examine the discriminant (b² - 4ac) before solving quadratics to instantly know if roots are real, distinct, repeated, or complex.
In statistical analysis, always check both the mean and median to identify if data distribution is skewed by outliers.
When calculating percentage changes, ensure you divide by the original starting baseline value: ((New - Old) / Old) * 100.

Frequently Asked Questions (FAQ)

Subtract the expected (true) value from the observed (measured) value, take the absolute value, divide by the expected value, and multiply by 100.

It depends entirely on the context — a percent error under 5% is often considered acceptable in a high-school science lab, while precision manufacturing or analytical chemistry may require error well under 1%.

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