Percentage Error Calculator
Enter your measured value and the accepted theoretical value to find out how accurate your measurement was. A result close to 0% means high accuracy. Used in chemistry, physics, engineering, and quality control wherever you need to validate a measurement against a known reference. The result is always positive because the formula uses absolute difference — direction doesn't matter, only the size of the deviation.
When to use this calculator
Use this in any situation where you have an expected value and need to evaluate how close your actual measurement came — a lab titration, a sensor reading against a calibrated standard, a model forecast versus actual outcome, or a student experiment checking against a textbook value.
Percentage Error
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Results are instant — nothing is stored and no account is needed.
Related Calculators
How to Calculate
- Enter the experimental value — the result you measured or observed.
- Enter the theoretical value — the accepted or expected correct value.
- The percentage error is calculated instantly.
Formula
Take the absolute difference between your measured and expected values, divide by the theoretical value, then multiply by 100. The absolute value ensures the result is always positive regardless of direction.
Examples
Experimental: 9.5, Theoretical: 10
5% error
Experimental: 102, Theoretical: 100
2% error
Experimental: 4.65, Theoretical: 5
7% error
Use Cases
- Checking the accuracy of lab measurements in chemistry or physics
- Validating sensor or instrument readings against calibrated values
- Assessing quality control tolerances in manufacturing
- Comparing model predictions to known outcomes
- Evaluating experimental results in academic coursework
FAQ
What is percentage error?
Percentage error measures how far an experimental or measured value is from the accepted theoretical value. It quantifies accuracy — the closer to 0%, the more accurate the measurement.
What is the percentage error if experimental is 9.8 and theoretical is 10?
The percentage error is 2%. Calculation: |9.8 − 10| / 10 × 100 = 0.2 / 10 × 100 = 2.
What is the percentage error if experimental is 105 and theoretical is 100?
The percentage error is 5%. Calculation: |105 − 100| / 100 × 100 = 5. This works the same whether the measurement is above or below the theoretical value.
What is a good percentage error?
Context-dependent. In most school lab experiments, under 5% is acceptable. In precision manufacturing or medical equipment, even 0.5% may be too high. In chemical titrations, under 1% is typical. Always check the acceptable tolerance for your specific application.
Why is percentage error always positive?
The formula uses the absolute value of the difference, so the sign of the error is discarded. This makes sense because accuracy is about magnitude, not direction — being 2% too high is as inaccurate as being 2% too low.
What is the difference between percentage error and percentage difference?
Percentage error requires a known correct value — it measures deviation from that reference. Percentage difference treats both values as equally valid and uses their average as the denominator. Use percentage error in scientific and engineering contexts where a true or accepted value exists.