Enter your measured value and the true value to find the percent error.

Measuring accuracy

Percent error compares a measured value against a known true value and expresses the gap as a percentage. It is the standard way to report accuracy in science labs, engineering, and manufacturing, because a raw difference means little without the scale of the true value.

Because it uses the absolute difference, percent error is always positive and says nothing about direction. A smaller percent error means a measurement closer to the accepted truth. Do not confuse it with percent difference, which compares two measurements when neither is treated as correct.

The formula

Worked example

Measured 48 against a true value of 50: error = |48 - 50| / 50 x 100 = 4%.

How to read your result

Percent error measures accuracy relative to the accepted value. A smaller percent error means a measurement closer to the truth. It is standard in lab reports and quality checks.

Frequently asked questions

Is percent error always positive?

Yes, because it uses the absolute difference.

What is a good percent error?

It depends on the field; many lab contexts accept a few percent.

How is it different from percent difference?

Percent error compares to a known true value; percent difference compares two measurements with no accepted truth.

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