Percent Error Calculator

Last Updated on March 2, 2026 | 2 : 54 pm by Anas Brittany

Use this percent error calculator to measure how far an observed (measured) value is from the true (accepted) value. It calculates percent error using the standard formula and also shows absolute error and relative error. You can optionally allow a signed percent error (negative results) to show whether the measurement is below or above the true value.

What Is Percent Error?

Percent error (also called percentage error) is a way to describe how far a measured or observed value is from the true (accepted) value, expressed as a percentage of the true value. A smaller percent error means the measurement is closer to the true value, while a larger percent error indicates the measurement is farther away.

Percent error is commonly used in science labs, engineering measurements, and classroom experiments where you compare results against an accepted value.

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Percent Error Formula

Percent error is calculated using the absolute difference between the observed and true values, divided by the true value, then multiplied by 100:

Percent Error = |Observed − True| / |True| × 100%

This method focuses on the size of the error (how far off the measurement is), not the direction.

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Absolute Error vs Relative Error vs Percent Error

These terms are closely related:

• Absolute error is the difference between the observed value and the true value: |Observed − True|
• Relative error is the absolute error divided by the true value: |Observed − True| / |True|
• Percent error is the relative error expressed as a percentage: (|Observed − True| / |True|) × 100%

If you want a quick interpretation: absolute error is the raw “amount off,” while percent error tells you how big that error is compared to the true value.

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Signed Percent Error and Negative Results

Percent error is usually reported as a positive number because the formula uses absolute value. However, some labs or classes allow a signed percent error to show direction:

Signed Percent Error = (Observed − True) / True × 100%

If the result is negative, the observed value is lower than the true value. If the result is positive, the observed value is higher than the true value.

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Example Percent Error Calculation

If an observed value is 56.891 and the true value is 62.327, the percent error is about 8.722%. This indicates the measurement is within roughly 9% of the accepted value.

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Frequently Asked Questions

What is a good percent error?

In general, a “good” percent error depends on the context, the tools used, and the required precision. In many lab settings, smaller is better, and large percent errors may suggest measurement issues or experimental limitations.

Can percent error be greater than 100%?

Yes. If the observed value is more than double the true value (or far smaller), percent error can exceed 100%.

Why can’t the true value be zero?

Because percent error divides by the true value. If the true value is 0, the percent error is undefined.