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Percent Error Calculator: Measured vs True Value

This free percent error calculator compares what you measured with the accepted value. It returns the percent error, absolute error and relative error, and shows the formula it used.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Percent error shows how far a measurement is from the right answer, as a share of the right answer. It is used in physics, chemistry and engineering labs to judge accuracy and to compare experiments of different sizes.

Enter your value and the accepted value, and read all the common error measures together.

How to Use This Tool

  1. Type your measured value.
  2. Type the true or accepted value.
  3. Press Calculate.
  4. Read the percent error and the absolute and signed errors.

How the Calculation Works

Absolute error = |measured − true|. Relative error = absolute error ÷ |true|. Percent error = relative error × 100. The signed error is measured − true, so a positive value means you measured too high.

Worked Example

A student measures gravity as 9.6 m/s² and the accepted value is 9.81. The absolute error is 0.21, the relative error is 0.0214 and the percent error is 2.14%. The signed error is −0.21, so the measurement was low.

Common Uses

  • Physics and chemistry lab reports.
  • Checking instruments against a standard.
  • Quality checks in manufacturing.
  • Comparing estimates with real results.

Tips and Common Mistakes

  • Use the accepted value in the denominator, not your own.
  • Keep the same units for both values.
  • Report the result with a sensible number of significant figures.

Next, you may need the percentage calculator, standard deviation calculator, average calculator, rounding calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

|measured − true| ÷ |true| × 100. The vertical bars mean the difference is taken as a positive number.
In most school labs it is reported as a positive number. This tool also shows the signed error so you can see whether you measured high or low.
It depends on the experiment. Under 5% is usually considered good in school labs, and professional work often needs far less.
The percent error is undefined because you cannot divide by zero. Use the absolute error instead.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.