Percent Error Calculator

Percent Error
5.00%
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📊 Details

Absolute Error–
Signed Error–

What Is Percent Error?

Percent error measures how far an experimental (measured) value differs from a theoretical (accepted or true) value, expressed as a percentage — widely used in science labs, engineering, and quality control to assess measurement accuracy.

How to Use the Percent Error Calculator

  1. Enter the theoretical (accepted or expected) value.
  2. Enter the experimental (measured or observed) value.
  3. View the percent error instantly.

Percent Error Formula

Percent Error
% Error = |Experimental − Theoretical| / |Theoretical| × 100

Worked Example

Example: Theoretical 100, Experimental 95

Absolute error: |95 − 100| = 5

Percent error: (5 / 100) × 100 = 5%

Understanding Your Results

Percent Error is always expressed as a positive percentage by convention (using absolute value), showing the magnitude of the discrepancy regardless of direction. Signed Error preserves whether the experimental value was higher or lower than theoretical, which can be useful diagnostic information.

Percent Error vs. Percentage Difference

Percent error specifically compares a measured value against a known "true" or accepted value. Percentage difference (or percentage change) more generally compares any two values without implying one is the accepted standard — the formulas are related but used in different contexts.

Common Mistakes to Avoid

  • Dividing by the experimental value instead of the theoretical value in the denominator.
  • Forgetting the absolute value, which can lead to a "negative percent error" that doesn't match standard convention.
  • Confusing percent error with percent difference when no true/accepted value exists to compare against.

Frequently Asked Questions

Subtract the theoretical value from the experimental value, take the absolute value, divide by the theoretical value, then multiply by 100.

This depends entirely on context — some scientific measurements require error under 1%, while other contexts may accept much higher error rates. There's no universal threshold.

By standard convention, percent error uses absolute value and is reported as a positive percentage. The signed error (without absolute value) can be negative, indicating the experimental value was lower than theoretical.

Percent error compares a measurement against a known true or accepted value. Percentage difference compares two values without one necessarily being the established standard.

It provides a standardized way to assess measurement accuracy and communicate how close experimental results come to expected or theoretical values.