Percent Error Calculator
Percent error, signed and absolute error, and percent difference, with working.
About this tool
Enter your measured or experimental value and the accepted or true value. The calculator shows the percent error with the formula filled in, the signed error showing whether you measured high or low, the absolute error in your original units and the percent difference between the two numbers.
How to calculate percent error
Percent error measures how far a result is from the accepted value, as a percentage of that value: |measured โ accepted| รท |accepted| ร 100. If a pendulum experiment gives g = 9.6 m/sยฒ and the accepted value is 9.81 m/sยฒ, the absolute error is 0.21 and the percent error is 0.21 รท 9.81 ร 100 = 2.14%. Most lab reports use the absolute value, so the percent error is always positive. Keeping the sign, here โ2.14%, tells you the measurement was low, which can point to a systematic error such as friction or a timing delay. Percent difference answers a different question: how far apart two measurements are when neither is the reference. It divides the gap by the average of the two values, so 9.6 and 9.81 differ by 2.16%. Percent change uses the signed formula to describe a value moving from an old figure to a new one. Honest limits: percent error is undefined when the accepted value is zero, and a small error in one trial doesn't prove a method is accurate. Repeat measurements and look at the spread as well. The percentage calculator handles general percentages and the sig figs calculator rounds results to the right precision.
Frequently asked questions
What is a good percent error?
It depends on the experiment. In school labs, under 5% is often considered good and under 1% excellent.
Can percent error be negative?
The standard formula uses an absolute value, so it is positive. The signed version is negative when the measurement is below the accepted value.
What is the difference between percent error and percent difference?
Percent error compares with an accepted value; percent difference compares two measurements using their average.
Is my data saved?
No. The calculation runs in your browser and nothing is stored or sent.