WorldCalcs

Percent Error Calculator

Compare a measured value to the accepted value to see how accurate your measurement is.

Reviewed by the WorldCalcs team · Methodology · Last reviewed: July 2026

Percent error

0.101937 %

Absolute error

0.01

Percent error is normally reported as a positive value.

What is percent error?

Percent error tells you how far a measured value is from the value that is accepted as correct, expressed as a percentage of that accepted value. It's the standard way to report accuracy in science classes and labs: after measuring something — the density of a metal, the acceleration of gravity, the boiling point of a liquid — you compare your result to the known, published figure. A small percent error means your measurement landed close to the accepted value; a large one points to a bigger discrepancy, whether from a measurement slip, an instrument limit, or an unexpected effect.

The percent error formula

The formula is percent error = |measured − true| ÷ |true| × 100 %. First take the difference between your measured (experimental) value and the true (accepted) value, then drop the sign by taking the absolute value — this is the absolute error. Divide that by the absolute value of the true value to see how big the gap is relative to what you expected, and multiply by 100 to turn it into a percentage. Because the difference is taken in absolute value, percent error is normally reported as a positive number; if you also care about direction, note whether your measurement came out higher or lower than the accepted value.

Worked example

Suppose you measure the acceleration of gravity as 9.8 m/s² and the accepted value is 9.81 m/s². The absolute error is |9.8 − 9.81| = 0.01. Dividing by the true value gives 0.01 ÷ 9.81 = 0.0010194, and multiplying by 100 gives a percent error of about 0.101937 %, or roughly 0.10 % — a very accurate measurement. As a second example, a measured value of 105 against a true value of 100 gives |105 − 100| ÷ 100 × 100 = 5 %. To turn any two numbers into a percentage difference of a different kind, see the percentage calculator; to judge how many digits of your answer are trustworthy, see the significant figures calculator. For spread across repeated measurements, the standard deviation calculator and the percentage increase calculator are useful too.

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Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer

How to use

Enter your measured (experimental) value and the true (accepted) value. The calculator returns the percent error and the absolute error using the formula |measured − true| ÷ |true| × 100 %.

Percent error is normally reported as a positive number. The true value can't be zero, since dividing by zero is undefined.

Frequently asked questions

What is the percent error formula?+

Percent error = |measured − true| ÷ |true| × 100 %. Subtract the accepted value from your measurement, take the absolute value, divide by the accepted value, and multiply by 100.

What's the difference between percent error and percent difference?+

Percent error compares a measurement to a known, accepted value. Percent difference compares two experimental values when neither is treated as the "true" one, and divides by their average instead.

How is percent error different from percentage change?+

Percentage change measures growth or decline from an old value to a new value over time. Percent error measures accuracy against a fixed accepted value; there's no "before and after."

Can percent error be negative?+

As defined here it's always positive because of the absolute value. Some courses keep the sign to show whether the measurement was too high (positive) or too low (negative) — the size is the same either way.

What counts as a good percent error?+

It depends on the field and the equipment. In many school experiments under about 5 % is considered good, but precise lab work may require a fraction of a percent. Always compare against the expectation for your specific measurement.

What's the difference between absolute error and percent error?+

Absolute error is the raw gap, |measured − true|, in the original units. Percent error scales that gap by the true value so you can compare accuracy across measurements of very different sizes.

Why can't the true value be zero?+

The formula divides by the true value, and dividing by zero is undefined. When the accepted value is zero, percent error can't be computed — use the absolute error instead.

Which value goes on top?+

The difference |measured − true| goes on top and the accepted (true) value goes on the bottom. Putting the true value in the denominator is what makes the result a fair measure of accuracy.

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