Percent Error Calculator
Calculate the percentage error between an experimental value and a theoretical value. Essential tool for chemistry, physics, and science labs to determine accuracy.
The measured or observed value from your experiment.
The accepted, known, or exact value.
What is Percent Error?
Percent Error (or percentage error) is a measure used in science and statistics to quantify how accurate a measured value is compared to a true or accepted value. It is expressed as a percentage of the true value.
A low percent error indicates that your experimental result is close to the accepted value (high accuracy), while a high percent error means there is a significant discrepancy.
Percent Error Formula
The calculation involves finding the absolute difference between the experimental and theoretical values, dividing by the theoretical value, and multiplying by 100.
% Error = |(Experimental - Theoretical) / Theoretical| × 100
- Experimental Value: The value you measured in the lab or observed.
- Theoretical Value: The known, accepted, or actual value found in textbooks or data tables.
- Absolute Bars (| |): The calculation uses the absolute value, meaning the result is always positive.
Example Calculation
Imagine you measured the boiling point of water to be 98°C. However, the known boiling point of water is 100°C.
- Subtract accepted from measured: 98 - 100 = -2
- Take the absolute value: |-2| = 2
- Divide by the accepted value: 2 / 100 = 0.02
- Multiply by 100: 0.02 × 100 = 2%
Your measurement had a 2% error.
Why is Percent Error Important?
In scientific experiments, measuring error is crucial for:
- Validating Results: Confirming if an experiment was conducted correctly.
- Instrument Calibration: Checking if measurement tools are accurate.
- Quality Control: Ensuring manufacturing processes stay within acceptable limits.
? Frequently Asked Questions
No. The standard formula uses absolute value bars around the difference (Experimental - Theoretical), so the final percentage is always positive. However, if you are calculating 'Percent Deviation' without absolute value, it can be negative to show if the value was lower than expected.
It depends on the field. In precision chemistry or physics labs, less than 5% is often expected. In biology or social sciences, errors up to 10% or even 20% might be acceptable due to natural variability.
Percent Error compares a measured value to a known 'true' value. Percent Difference compares two measured values to each other (where neither is considered the 'true' standard).