Percent Error Calculator

Observed / Measured Value

True / Accepted Value

Percent error is undefined when the true value is 0.

Decimal Places

Controls formatting of results only.

Formula: |Observed − True| ÷ |True| × 100% (absolute percent error)

Percent Error – Quick Cheat Sheet

Absolute error: Observed − True. Magnitude |Observed − True|.
Percent error (absolute): |Observed − True| ÷ |True| × 100%.
Percent error (signed): (Observed − True) ÷ |True| × 100% (indicates direction).
Relative error (unitless): |Observed − True| ÷ |True|.
Zero true value: percent/relative error are undefined when True = 0.
Rounding: Choose decimal places to control display formatting only.

Tips & notes

Use absolute percent error when you only care about magnitude; use signed when direction matters.
For very small accepted values, percent error can become large—check units and measurement method.
Report both measured and accepted values alongside the percent error for clarity.

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