Percent Error Calculator
Percent error tells you how far a measured or estimated value is from the accepted value, relative to the size of the accepted value. Enter both numbers to get the percent error, the signed error and the absolute error.
- Signed error
- -2.1407%
- Absolute error
- 0.21
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Enter the value you measured, calculated or estimated.
- Enter the accepted, theoretical or true value.
- Read the percent error. The signed error shows whether you were too high (positive) or too low (negative).
Worked examples
Measuring g as 9.6 m/s² against 9.81
- Percent error
- 2.1407%
- Signed error
- -2.1407%
- Absolute error
- 0.21
An estimate of 52 when the true value is 50
- Percent error
- 4%
- Signed error
- 4%
- Absolute error
- 2
Reading the result
Percent error is normally reported as a positive number, which is the headline result here. The signed version is useful when you want to spot a consistent bias — a scale that always reads 2% high, for example.
There is no universal cutoff for a “good” percent error. It depends on the instrument and the experiment: a kitchen scale and an analytical balance are held to very different standards.
Common mistakes
Divide by the accepted value, not by your measurement. Keep both values in the same unit. And if the accepted value is zero, percent error is undefined — report the absolute error instead.
Questions people ask
What is the percent error if I measure 9.6 and the true value is 9.81?
2.14%. The absolute error is 0.21, and 0.21 ÷ 9.81 = 0.0214.
Can percent error be negative?
By the usual definition it is an absolute value, so no. Some teachers ask for the signed error, which is negative when the measurement is below the accepted value; this calculator shows both.
What is the difference between percent error and percent difference?
Percent error compares a measurement with a known correct value. Percent difference compares two measurements when neither is known to be correct, using their average as the base.