Enter your Experimental Value and Accepted/True Value into the Percent Error Calculator to find how far off your measurement really is — the tool returns your Percent Error, Absolute Error, and optionally a Signed Percent Error so you can see not just the magnitude but the direction of your mistake.
Percent Error
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Absolute Error
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Signed Percent Error
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Percent error measures the relative difference between an experimental (measured) value and an accepted (true) value. It's important because it quantifies the accuracy of measurements and helps assess whether experimental results are reliable.
Percent error is calculated using the formula: |Experimental Value - Accepted Value| / |Accepted Value| × 100%. The absolute value ensures the result is always positive unless you're calculating signed percent error.
Percent error compares a measured value to a known true value, while percent difference compares two measured values when there's no established 'true' reference value. Use percent error when you have an accepted standard.
Percent error can result from instrument limitations, human error, environmental conditions, systematic errors in methodology, or natural variation in the quantity being measured.
Acceptable percent error depends on the field and precision required. In general, less than 5% is considered good for most scientific measurements, while less than 1% indicates high accuracy.
Standard percent error is always positive due to the absolute value in the formula. However, signed percent error can be negative, indicating whether the experimental value is below (negative) or above (positive) the accepted value.
Absolute error is the simple difference between experimental and accepted values, while percent error expresses this difference as a percentage of the accepted value, making it easier to compare errors across different scales.