About this Percent Error
In science labs (chemistry, physics), calculating Percent Error is essential to determine how accurate your experimental results are. It tells you how far off your measured value is from the true or accepted value, expressed as a percentage.
Who this calculator is for
- Students writing chemistry or physics lab reports.
- Teachers checking measurement accuracy in classwork and experiments.
- Anyone comparing a measured value against an accepted benchmark.
When to use it
- Use this calculator when you have an accepted value and a measured value.
- Use it to report how far an experiment or estimate is from the target value.
- Use it to check accuracy in lab work, homework, or simple measurement comparisons.
How to use this calculator
- Enter the Theoretical Value (the 'correct' or accepted value found in textbooks).
- Enter the Experimental Value (the value you measured in the lab).
- The result is your Percent Error.
Key assumptions
- The theoretical value is the accepted baseline for the calculation.
- The result reports error magnitude, so it is always positive.
- Both values should use the same unit before you compare them.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
The formula for Percent Error is:
$\text{Percent Error} = \left| \frac{\text{Experimental} - \text{Theoretical}}{\text{Theoretical}} \right| \times 100$
The absolute value bars mean the result is always positive.
Inputs explained
Theoretical Value
The actual, exact, or accepted value. This is the standard you are comparing against.
Experimental Value
The value derived from observation, calculation, or experimentation.
Understanding your results
A low percent error (e.g., < 5%) means your result is very accurate. A high percent error suggests systematic or random errors in your experiment.
Example scenarios
Chemistry Lab
Theoretical yield 10g. You produced 9g. Difference is 1g. Percent Error = (1/10) * 100 = 10%.
Physics
Gravity is 9.8 m/s². You measured 9.6 m/s². Percent Error = |(9.6 - 9.8) / 9.8| * 100 ≈ 2.04%.
Key Features
- Absolute Value Logic
- Instant Percentage
- Lab Report Ready
Tips & Best Practices
- Always use the absolute value. Error magnitude matters more than direction (positive/negative) for this metric.
- Check your units! Ensure both values are in the same unit (e.g., grams, meters) before calculating.
Glossary of Terms
- Accuracy
- How close a measurement is to the true value.
- Precision
- How consistent repeated measurements are (not the same as accuracy).