Percent Error Calculator
Calculate the percent error between an experimental (measured) value and a theoretical (expected) value.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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This calculator finds the percent error between a measured (experimental) value and a known (theoretical) value. Enter both values and the result appears instantly.
- Enter the experimental value. This is the value you measured, observed, or calculated in your experiment or analysis.
- Enter the theoretical value. This is the accepted, known, or expected value that you are comparing against.
- Read the result. The percent error and absolute error appear immediately. The result shows how far off your measurement was as a percentage of the theoretical value.
The formula is: |Experimental - Theoretical| / |Theoretical| x 100. The absolute value signs ensure the result is always positive, representing the magnitude of the error regardless of direction.
About Percent Error
Percent error is a standard measure used in science, engineering, and statistics to express how far a measured value deviates from a known or accepted value. It gives context to raw errors by expressing them relative to the expected value. A 2-unit error means very different things depending on whether the expected value is 10 or 10,000.
In laboratory settings, percent error helps evaluate the accuracy of experimental methods. In quality control, it measures how close manufactured items are to their specifications. Lower percent error generally indicates better accuracy and more reliable methods.
Frequently Asked Questions
What is a good percent error?
What counts as acceptable depends on the field. In chemistry labs, under 5% is often considered good. In physics experiments, under 1-2% may be expected. In manufacturing, tolerances vary widely by industry and product specifications.
Can percent error be negative?
The standard percent error formula uses absolute values, so the result is always positive. Some fields use a signed version to indicate whether the measurement was above or below the expected value, but this calculator uses the unsigned (absolute) form.
What if the theoretical value is zero?
Percent error is undefined when the theoretical value is zero because the formula requires dividing by the theoretical value. In this case, use absolute error instead, which is simply the difference between the two values.