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Percent Error Calculator

Experimental (measured) value

Theoretical (accepted) value

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Cos'è Percent Error Calculator?

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Percent error measures the accuracy of an experimental or measured value compared to an accepted or theoretical value. It expresses the discrepancy as a percentage, making it easy to compare errors across different scales and units.

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Come Percent Error Calculator

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1Percent error = |Experimental − Theoretical| / |Theoretical| × 100%
2The absolute value removes the sign — percent error is always positive
3Signed percent error indicates direction: positive = measured too high, negative = too low
4Used in chemistry, physics, engineering, and manufacturing quality control

Esempi risolti

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Esempio 1

Dato:Measured density: 9.7 g/cm³, True density: 10.0 g/cm³

Risultato:3.0% error

|9.7−10| / 10 × 100 = 3%

Esempio 2

Dato:Predicted 50, actual 47

Risultato:6.0% error

|50−47| / 47 × 100 = 6.38%

Acceptable Percent Error by Application

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Field	Typical acceptable error	Notes
Pharmaceutical manufacturing	<1%	Active ingredient content
Engineering / machining	<0.1–2%	Depends on tolerance
Chemical lab experiments	<5%	Educational context
Survey / opinion polls	±3–5%	Sampling error
Medical diagnostics	<5%	Varies by test type
Weather forecasting (24hr)	<10%	Temperature predictions

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Consiglio Pro

Percent error uses the theoretical (accepted) value in the denominator, not the experimental value. Using the wrong denominator is a common mistake that gives a different — and incorrect — result.

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Lo sapevi?

NASA's Mars Climate Orbiter was lost in 1999 due to a unit conversion error — one team used metric units while another used imperial. The spacecraft was $327 million. The percent error in trajectory was small, but catastrophic at interplanetary scale.

Riferimenti

›Approximation error — Wikipedia

Mathematically verified

Reviewed October 2026

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Percent Error Calculator