Percent error calculator guide

How to use the Percent Error Calculator

The Percent Error Calculator compares a measured or experimental value with an accepted, true, or theoretical value. It shows the standard absolute percent error, signed percent error, absolute error, relative error, and the steps behind the result.

Open the percent error calculator

Quick start

Enter your measured or experimental value.
Enter the accepted, true, reference, or theoretical value.
Add a unit label if the values have units, such as cm, g/cm3, or mL.
Press Calculate percent error.
Review the percent error, signed percent error, absolute error, and steps.

The formula

The standard percent error formula is the absolute value of measured minus accepted, divided by the absolute value of the accepted value, multiplied by 100.

In plain words: find how far your result is from the accepted value, compare that difference with the accepted value, then write the comparison as a percent.

Measured and accepted values

The measured value is the result you observed, tested, or calculated in an experiment. It may also be called the experimental value.

The accepted value is the reference value you are comparing against. In science classes, this could be a textbook value, teacher-provided value, theoretical value, or known standard.

Signed percent error

Standard percent error is usually positive because it uses absolute error. Signed percent error keeps the direction: a positive result means the measured value was high, while a negative result means the measured value was low.

Use the absolute percent error when your assignment asks for percent error. Use the signed percent error when you also need to explain whether the measurement was above or below the accepted value.

Examples

2.45 vs 2.70 Density-style lab example with about 9.259% percent error.

48 vs 50 A measurement that is low by 2 units and has 4% percent error.

105 vs 100 A high reading with 5% percent error and signed percent error of +5%.

Examples from the percent error calculator

Density lab Measured 2.45 vs accepted 2.70

9.25925925926% error

Length measurement Measured 48 vs accepted 50

4% error

High reading Measured 105 vs accepted 100

5% error, signed +5%

Common mistakes to avoid

Make sure the measured value and accepted value use the same unit before calculating. Do not compare centimeters with meters or grams with kilograms until they are converted into the same unit.

The accepted value cannot be zero because the formula divides by the accepted value. If the accepted value is zero, percent error is undefined.

History, privacy, and copying

Recent percent error answers stay visible in the page while you work. The history is kept only in the current browser tab and is not sent to a server.

Copy answer copies the percent error, signed percent error, and absolute error so you can paste the result into notes, homework, or a lab report draft.