Percent Error Calculator
The percentage difference between a measured value and the true value.
Result
Percent error (%)
2.00
How it works
Percent error measures how far a measurement strayed from the true value: |measured − actual| ÷ |actual| × 100. Measure 9.7 where the accepted value is 10 and the error is 3%. The absolute value is what makes it an error rather than a deviation — it does not matter whether you overshot or undershot, only by how much. If you do need the direction, drop the absolute value and the sign tells you: negative for an underestimate, positive for an overestimate. This is the standard way lab reports quantify accuracy. Below 5% is usually considered good for a school experiment; above that suggests a systematic problem — an uncalibrated instrument, a consistent reading bias or a flawed method. And yes, it can exceed 100%: measure 25 where the true value is 10 and the error is 150%.
Advertisement
Frequently asked questions
How is percent error calculated?
Take the absolute difference, divide by the true value, multiply by 100.
Can it be over 100%?
Yes — if the measurement is more than double the true value.
What counts as an acceptable percent error?
It depends on the field. School lab work often accepts under 5%; precision engineering and analytical chemistry demand far less. A large error usually points to a systematic fault rather than random noise.
Advertisement