Percent Error Calculator
Calculate percent error between experimental and theoretical values.
A percent error calculator measures the accuracy of an experimental value by comparing it to a known theoretical value.
Examples
Chemistry lab
Physics experiment
Large error
Frequently Asked Questions
What is percent error?
Can percent error be negative?
What is a good percent error?
Quick Tips
- •Double-check your inputs — small errors lead to incorrect results.
- •Use decimal form for fractions when entering values.
- •Compare your percent error to accepted thresholds for your field to judge result quality.
A percent error calculator measures the accuracy of an experimental value by comparing it to a known theoretical value.
How to Use This Calculator
Enter the experimental (measured) value and the theoretical (accepted) value. The calculator will compute the percent error, absolute error, and relative error.
Understanding the Formula
Percent Error = |Experimental - Theoretical| / |Theoretical| × 100%
Examples
Chemistry lab
Measured boiling point 99.1°C vs theoretical 100°C: Error = |99.1-100|/100 × 100 = 0.9%
Physics experiment
Measured gravity 9.7 m/s² vs 9.8 m/s²: Error = |9.7-9.8|/9.8 × 100 = 1.02%
Large error
Measured 15 vs theoretical 10: Error = 5/10 × 100 = 50%
Frequently Asked Questions
What is percent error?
Percent error measures how far an experimental value is from the accepted (theoretical) value, expressed as a percentage of the theoretical value.
Can percent error be negative?
By convention, percent error uses absolute value and is always non-negative. Some fields use signed error to indicate direction.
What is a good percent error?
It depends on the field. In chemistry labs, under 5% is typically acceptable. In precision engineering, much lower errors are expected.
Assumptions & Limitations
- Assumes the theoretical value is not zero; division by zero is undefined.
- Assumes exact input values; rounding in inputs propagates to results.
- Uses absolute value by default, so the result is always non-negative.