Percent Error Calculator — Formula with Step-by-Step Solution

Calculate percent error between a theoretical (accepted) value and an experimental (measured) value. See the full formula breakdown with step-by-step solution. Perfect for science labs, physics, chemistry, and engineering. 100% free, no sign-up.

Theoretical / Accepted Value

The known or true value

Experimental / Measured Value

The value you measured or observed

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Free Percent Error Calculator Online

OptiDrop's Percent Error Calculator computes the percentage difference between a theoretical (accepted/true) value and an experimental (measured/observed) value. It's an essential tool for students, scientists, and engineers who need to evaluate the accuracy of their measurements.

How to Calculate Percent Error

The percent error formula is: % Error = |Experimental - Theoretical| / |Theoretical| × 100. First, find the absolute difference between the two values. Then divide by the theoretical value. Finally, multiply by 100 to get the percentage. This calculator shows every step of the calculation.

When to Use Percent Error

Percent error is commonly used in science labs to evaluate measurement accuracy, in engineering to assess tolerance levels, in manufacturing for quality control, and in academic research to validate experimental results. A lower percent error indicates a more accurate measurement.

Frequently Asked Questions

The percent error formula is: % Error = |Experimental Value - Theoretical Value| / |Theoretical Value| × 100. The absolute value ensures the result is always positive. This measures how far your experimental measurement deviates from the accepted or true value.

The absolute value is used because percent error measures the magnitude of the error, not the direction. Whether your experimental value is higher or lower than the theoretical value, the percent error tells you how far off you are in percentage terms. The result is always a positive number.

What counts as a good percent error depends on the field. In chemistry and physics labs, 5% or less is generally considered good. In engineering, 1-2% may be required. In some social sciences, 10-15% may be acceptable. Generally, lower percent error indicates more accurate measurements.

Last updated: June 2026