Percent error calculator
Find how far a measured result is from the accepted value. Chemistry and physics students use it most often for lab reports.
- Runs in your browser
- Free, no account needed
- Copy or download the result
Result
Example
Experimental (measured) value: 9.6 Theoretical (accepted) value: 9.81 Result sign: Absolute value (always positive)
Percent error: 2.140672783% Absolute error |experimental - theoretical|: 0.21 Relative error: 0.02140672783 Formula: |9.6 - 9.81| / |9.81| × 100
How to use the percent error calculator
- Type the Experimental (measured) value and the Theoretical (accepted) value.
- Choose a Result sign: Absolute value or Signed.
- Press Run to see the percent error, absolute error and relative error.
- Press Copy result or Download to paste the numbers into your report.
How it works
Percent error = |experimental - theoretical| / |theoretical| x 100. Relative error is the same value before multiplying by 100.
Signed mode keeps the sign of experimental - theoretical, so a negative result means your measurement was below the accepted value.
The theoretical value cannot be 0, because the formula divides by it. Results are rounded to 10 significant digits.
Everything runs in your browser. Your input is not uploaded or stored.
Questions and answers
What is the formula for percent error?
Subtract the accepted value from your measured value, take the absolute value, divide by the accepted value and multiply by 100.
Can percent error be negative?
With the usual definition it is always positive. Some teachers want the signed version to show whether you were high or low, so choose Signed.
What is a good percent error?
It depends on the experiment and the equipment. Check your lab manual or ask your teacher for the expected range.