Percent Error Calculator

How to use this calculator

Enter the measured value and the true (accepted or reference) value. The absolute difference and percent error appear instantly. You can also work backwards to find the measurement range allowed by a given error.

The formula

% error = |measured − true| ÷ |true| × 100

Worked example

A student measures gravity as 9.6 m/s². The accepted value is 9.81 m/s².

• Difference = 9.6 − 9.81 = −0.21 (the measurement was low)
• Percent error = 0.21 ÷ 9.81 = 2.14%

Percent error vs percent change

• Percent error compares a measurement with a known correct value.
• Percent change compares a new value with an old one — use the percentage change calculator.

Accuracy specs in instrumentation

Instrument accuracy is often given as a percentage of reading or of span. A 0–10 bar transmitter with ±0.5% of span accuracy can be off by ±0.05 bar anywhere in its range — which is ±1% at a 5 bar reading and ±5% at 1 bar.

Frequently asked questions

What is the percent error formula?

Percent error = |measured − true| ÷ |true| × 100. Measuring g as 9.6 m/s² when it is 9.81 gives 2.14% error.

Can percent error be negative?

The standard form uses the absolute value, so it is always positive. The signed difference (shown as absolute error here) tells you whether the measurement was high or low.

What is a good percent error?

It depends on the field. School experiments often aim for under 5%; industrial instruments are often specified at 0.1–1% of reading or span.

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