Percent Error Calculator — Experimental vs True Value

Percent Error Calculator

Percent error compares a measured (experimental) value to a reference (true or accepted) value. Enter both numbers to see absolute error, relative error as a decimal, and percent error—standard steps on many science and maths mark schemes without substituting for method taught by your teacher.

Measured (experimental) value

The value you obtained from an experiment or estimate.

Reference (true/accepted) value

Known, literature, or target value you are comparing against.

The reference value cannot be zero when computing percent error.

How it works

Percent error compares a measured (experimental) value to a reference (true or accepted) value. Enter both numbers to see absolute error, relative error as a decimal, and percent error—standard steps on many science and maths mark schemes without substituting for method taught by your teacher.

The Formula

Absolute error = |measured − reference|

Relative error = absolute error ÷ |reference|

Percent error = relative error × 100%

Worked Example

Lab-style check
If you measure 24.8 g but the accepted value is 25.0 g, absolute error is |24.8 − 25.0| = 0.2 g. Relative error is 0.2 ÷ 25.0 = 0.008, so percent error is 0.8%.

Tips, Assumptions & Limitations

Use the accepted or true value as reference, not the other way round.
If the reference is exactly zero, percent error is undefined—you cannot divide by zero.
Percent error is always non-negative because we use the absolute difference.

FAQ

Compute absolute error as the absolute difference between your measured value and the reference value, divide by the absolute value of the reference, then multiply by 100 to express it as a percentage.

Percent error divides by the reference, so a reference of zero is not allowed here. Use a different summary, such as absolute error only, or follow your course’s guidance for that special case.

Yes if you have a clear reference and a measured figure—examples include a budget target in $ or £ versus what you spent, or a target mark versus the mark you earned. This tool does not estimate taxes or official grades; it only applies the formula you enter.

They are related but not identical. Percent error usually compares a measurement to an accepted true value, while percent difference often compares two measurements to each other. Use the definition your scheme specifies.