Percent error calculator guide

Percent Error Calculator Guide

Percent error is what you use when your lab result is close, but not perfect. If you measured a density of 2.45 g/cm3 and the accepted value is 2.70 g/cm3, this guide shows how far off the result is and whether your reading was high or low.

Open the percent error calculator

Smoke mascot explaining percent error formula steps with density, length, volume, and boiling-point examples beside high and low result arrows. — Percent Error Calculator guide artwork supports the walkthrough by showing measured-versus-accepted values, same-unit checks, signed error, zero-value limits, and lab-report cautions. View in the smoke-kawaii gallery

Quick start

Enter the value you measured, tested, or calculated.
Enter the accepted value from your table, teacher, textbook, or reference.
Add the unit label if it helps, such as cm, g/cm3, mL, or C.
Press Calculate percent error.
Check the absolute percent error, signed percent error, absolute error, and steps.

Percent error formula

The standard formula is |measured value - accepted value| / |accepted value| x 100. That gives the absolute percent error, so the answer is normally positive.

The calculator also shows signed percent error. Signed error keeps the direction: negative means your measured value was low, and positive means it was high.

Measured value vs accepted value

The measured value is your result. It might come from a scale, ruler, thermometer, beaker, calculator, or experiment.

The accepted value is the number you are checking against. In class, this is often a reference value from the lesson, a known standard, or a theoretical value your teacher gives you.

Example: density result

Say your measured density is 2.45 g/cm3 and the accepted density is 2.70 g/cm3. The error is 2.45 - 2.70 = -0.25 g/cm3.

The absolute error is 0.25 g/cm3. Divide 0.25 by 2.70, then multiply by 100. The percent error is about 9.2593%. The signed percent error is -9.2593%, so the measured value was low.

Examples

2.45 g/cm3 vs 2.70 g/cm3 Density lab check with 9.2593% error and a low signed result.

48 cm vs 50 cm Length measurement that is low by 2 cm and has 4% error.

105 mL vs 100 mL High reading with 5% error and signed percent error of +5%.

99.1 C vs 100 C Boiling-point check with 0.9% error and a low signed result.

Examples from the percent error calculator

Density lab check Measured 2.45 g/cm3 vs accepted 2.70 g/cm3

9.2593% error, signed -9.2593%

Length measurement Measured 48 cm vs accepted 50 cm

4% error, signed -4%

High volume reading Measured 105 mL vs accepted 100 mL

5% error, signed +5%

Boiling point check Measured 99.1 C vs accepted 100 C

0.9% error, signed -0.9%

Common mistakes to avoid

Match the units first. Do not compare centimeters with meters, grams with kilograms, or C with F until both values use the same unit.

Do not put the accepted value in the measured-value box by accident. The absolute percent error will match, but the signed percent error will point the wrong way.

The accepted value cannot be zero because the formula divides by it. If your accepted value is zero, percent error is undefined, so use another comparison your class allows.

What percent error does not prove

Percent error tells you how far one result is from an accepted value. It does not prove why the error happened. A bad reading, rounded input, wrong unit, dirty equipment, or a real experimental limit could all change the answer.

For a stricter lab report, percent error may not be enough by itself. OpenStax explains that measurement work also needs accuracy, precision, and uncertainty. Use those ideas if your teacher asks for a better error discussion.

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.