Calculate percent error between experimental and theoretical values. Step-by-step formula with chemistry and physics examples.
Real-World Scenario Presets
Show Signed Percent Error
Show whether experimental is above (+) or below (−) theoretical
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Percent error measures how close an experimental result is to a theoretical or accepted value, expressed as a percentage. It is widely used in chemistry, physics, and biology labs, as well as engineering and quality control. Enter your experimental and theoretical values above to calculate percent error instantly with full step-by-step workings.
Percent error (also called percentage error) quantifies the discrepancy between a measured or experimental value and an accepted or theoretical value, expressed as a percentage of the theoretical value. A lower percent error indicates a more accurate measurement. A percent error of 0% means perfect agreement with the accepted value.
Percent Error Formula
Skip the manual arithmetic. Enter your measured and accepted values to get percent error, absolute error, and relative error in one click.
Toggle between absolute (unsigned) and signed results to see whether your measurement was above or below the expected value, not just how far off.
Every calculation shows the full percent error formula so students can learn the method and verify each arithmetic step.
Instantly see whether your error is Excellent (< 1%), Acceptable (< 5%), High (< 10%), or Very High so you know when to revisit your method.
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Quickly verify percent error calculations, check your arithmetic, and learn the standard formula step by step.
Yes, if you use the signed formula without absolute value bars. A negative percent error means your experimental value was lower than the theoretical value. The standard unsigned formula always gives a positive result, which is what most textbooks and lab reports expect.
In most school science labs, a percent error under 5% is considered acceptable. For analytical chemistry or precision engineering, under 1% is typically expected. What counts as good depends on the measurement technique, equipment, and field — always check your course or industry guidelines.
Percent error compares a measured value to a known theoretical or accepted value using the theoretical value as the denominator. Percent difference compares two measured values when there is no known correct answer, using the average of both as the denominator. They are not interchangeable.
A percent error of 0% means your experimental value exactly equals the theoretical value — a perfect measurement with no discrepancy. This is rare in practice due to instrument limitations, rounding, and human error.
The standard percent error formula is: Percent Error = |Experimental Value − Theoretical Value| ÷ |Theoretical Value| × 100%. The absolute value bars ensure the result is always positive. For a signed version, remove the absolute value bars from the numerator.
Absolute error is the raw numerical difference between your experimental and theoretical values: |E − T|. Percent error normalizes this by the theoretical value and expresses it as a percentage, making it comparable across different scales, units, and experiments.