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Percent Error Calculator
Percent error shows how far a measured value is from the true or theoretical value. It is used in physics, chemistry and engineering labs.
Accuracy Precision Lab
Experimental Drift & Error Quantification
About the Percent Error Calculator
Percent error shows how far a measured value is from the true or theoretical value. It is used in physics, chemistry and engineering labs.
How to use the Percent Error Calculator
- Enter the Theoretical Value and the Experimental Value.
- Optionally set a Tolerance (%).
- Press Calculate percent error to see the error and whether it is within tolerance.
Formula and method
Percent error = |Experimental − Theoretical| ÷ |Theoretical| × 100
Worked example
If g is theoretically 9.81 m/s² and you measure 9.60, the error is 0.21 ÷ 9.81 × 100 ≈ 2.14%.
Gravity in a lab. A measured 9.80 m/s² against an accepted 9.81 m/s² gives |9.80 − 9.81| ÷ 9.81 × 100 = about 0.10%.
When to use the Percent Error Calculator
- Comparing a measured value with the accepted value in a science lab.
- Checking how accurate an estimate or a forecast was.
- Reporting experimental accuracy.
Common mistakes to avoid
- Dividing by the measured value instead of the accepted value.
- Forgetting to take the absolute value when you only need the size of the error.
Tips
- A smaller percent error means a more accurate measurement.
- Repeat measurements and average them to reduce random error.
Frequently asked questions
Can percent error be negative?
It is usually reported as an absolute value. Some labs keep the sign to show whether the result was high or low.
What is a good percent error?
It depends on the experiment. Under 5% is often considered good in a school lab, and precision work needs much less.
What is the difference between error and percent error?
The error is the raw difference. The percent error shows it as a share of the true value, which makes different measurements comparable.