How to calculate percent error
Percent error is commonly expressed as an absolute value so that over- and under-estimates produce the same positive result. It is calculated by taking the absolute difference between the experimental and theoretical values, dividing by the absolute value of the theoretical value, and multiplying by 100. A result of 0% means the measurement matched the accepted value exactly.
The distinction between absolute error and relative error is important. Absolute error is the raw difference in the same units as the measurement. Relative error normalises this by the size of the theoretical value, allowing meaningful comparison across measurements of very different magnitudes. Percent error is simply relative error expressed as a percentage.
Percent error = (|experimental - theoretical| / |theoretical|) x 100
The absolute difference between experimental and theoretical values, divided by the theoretical value, expressed as a percentage.
Absolute error = |experimental - theoretical|
The raw magnitude of the difference between the measured and accepted value, in the same units as the measurement.
Relative error = |experimental - theoretical| / |theoretical|
Absolute error normalised by the theoretical value, producing a dimensionless ratio.