WorkedMathGlossary

Percent Error Calculator

Enter your experimental and theoretical values below to instantly get the percent error.

Percent Error
4%

How Percent Error Is Calculated

Percent error = |experimental − theoretical| ÷ |theoretical| × 100. The absolute value bars mean the sign of the difference doesn't matter — only how far off the measurement was, as a share of the accepted value.

Worked example

A lab measures the boiling point of water as 98°C, when the accepted value is 100°C.

Percent error = |98 − 100| ÷ |100| × 100 = 2 ÷ 100 × 100

Percent error: 2%

Frequently Asked Questions

What is percent error?

Percent error measures how far a measured or experimental value is from the accepted or theoretical value, as a percentage of that theoretical value. It's used to judge how accurate a measurement or experiment was.

Why does percent error use absolute value?

Absolute value strips out the sign so percent error always reports how far off a value is, not whether it was too high or too low. Without it, a measurement 10% too high and one 10% too low would report as +10% and −10%, when what usually matters is just the size of the error.

What's a "good" percent error?

It depends entirely on the field and the equipment involved. A percent error under 5% is often considered acceptable in a high school science lab, while precision manufacturing or physics research may require error well under 1%. There's no universal cutoff.

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

Percent error compares a measured value to one known, accepted value (like a textbook constant). Percent difference compares two measured values to each other when neither is known to be more "correct" than the other, and typically divides by the average of the two instead of one fixed value.

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