Experimental value (measured)
Theoretical value (accepted/true)
Result with formula (click to copy)
Frequently Asked Questions
What is percentage error?
Percentage error measures how close an experimental measurement is to the true (theoretical) value. Formula: % Error = |Experimental − Theoretical| / |Theoretical| × 100. It is always expressed as a positive value.
What is a good percentage error?
In most school labs: <1% = excellent, 1–5% = good, 5–10% = acceptable. Above 10% usually means something went wrong with the experiment — check your method, equipment calibration, or calculations. Different fields have different tolerances.
What is the difference between error and uncertainty?
Error compares your result to a known value. Uncertainty describes the range of possible values in a single measurement. Error tells you how accurate your experiment was. Uncertainty tells you how precise your instruments are.
Why do we use absolute value in the formula?
Because error is always positive — it represents a magnitude of difference, not a direction. Whether your result is higher or lower than the true value, the error amount is the same. Removing the sign makes comparison between different experiments meaningful.