Percent Error Calculator
Calculate the percentage error between an experimentally observed measurement and the accepted, theoretical, or true benchmark value in physics, chemistry, and engineering laboratory experiments.
The value observed or recorded in your test/experiment
The standard accepted, known, or true physical value
Relative inaccuracy (|E − T| / |T|) × 100%
How to Use This Calculator
- Enter your experimentally measured value (E).
- Enter the accepted theoretical standard value (T).
- Inspect the resulting percent error, absolute discrepancy, and experimental accuracy.
Formula & Calculation Methodology
Percent error takes the absolute difference between the experimental reading and the accepted standard, divided by the absolute theoretical value, scaled to 100%.
Worked Example
Measuring gravitational acceleration g = 9.6 m/s² (Theoretical = 9.8 m/s²)
Chemical boiling point test 98.5°C vs 100.0°C water standard
Frequently Asked Questions
Why does percent error use absolute values?↓
In standard scientific laboratory convention, error magnitude is conventionally reported as a positive percentage, while direction is stated separately as over- or under-estimation.
Can percent error exceed 100%?↓
Yes. If an experimental value is more than double the theoretical value (e.g. measuring 25 when the true value is 10), percent error will be 150%.
What occurs if the theoretical value is zero?↓
Division by zero is undefined. Relative percent error cannot be computed against zero, but the absolute error is still reported.
What is an acceptable percentage error in lab experiments?↓
Introductory physics and chemistry labs typically consider error under 5% excellent and under 10% acceptable, depending on instrument tolerances.
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Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.