Percent Error Calculator
Enter the experimental (measured) and theoretical (accepted) values to instantly find the percent error.
What is Percent Error?
Percent error is a measure of how inaccurate a measurement is, compared to the true (accepted) value. It is widely used in scientific experiments, engineering, and quality control to assess the accuracy of an observed result. The smaller the percent error, the closer the experimental value is to the theoretical value.
Percent Error Formula
Percent Error = | (Experimental Value – Theoretical Value) / Theoretical Value | × 100%
The vertical bars indicate the absolute value, meaning we always treat the difference as positive. This gives us the magnitude of the error, ignoring direction.
How to Calculate Percent Error (Step-by-Step)
- Subtract the theoretical (true) value from the experimental (measured) value.
- Take the absolute value of the difference. This is the absolute error.
- Divide the absolute error by the absolute value of the theoretical value.
- Multiply the result by 100 to express it as a percentage.
Example Calculation
You measure a piece of wood and get 23.5 cm. The actual length is 25.0 cm. What is the percent error?
- Absolute error = |23.5 – 25.0| = 1.5 cm
- Percent error = (1.5 / 25.0) × 100% = 6.0%
A 6% error tells you that your measurement was off by 6% of the true value.
Use the calculator above to quickly check any values. Bookmark this tool for your lab reports and homework!
