About Percent Error Calculator

Percent error is a measurement of how inaccurate a measurement is, compared to the true or accepted value. It's commonly used in scientific experiments, quality control, and data analysis to quantify the accuracy of measurements. Our percent error calculator makes these calculations quick and easy.

How to Calculate Percent Error

The percent error formula is:

Percent Error = |(Observed Value - True Value)| / True Value × 100%

Where:

Observed Value is your experimental measurement
True Value is the known or theoretical value
The vertical bars | | mean absolute value (always positive)

Interpretation of Results

Percent error helps you understand the accuracy of your measurements:

0% error means perfect accuracy
Small error (under 5%) indicates good accuracy
Large error (over 10%) suggests potential problems with measurement

Practical Examples

Chemistry Experiment

True value: 250 mL (expected volume)

Observed value: 243 mL (measured volume)

Percent error: |(243 - 250)| / 250 × 100 = 2.8%

Physics Measurement

True value: 9.8 m/s² (gravity acceleration)

Observed value: 10.2 m/s² (measured acceleration)

Percent error: |(10.2 - 9.8)| / 9.8 × 100 = 4.08%

Quality Control

True value: 500g (product weight specification)

Observed value: 512g (actual measured weight)

Percent error: |(512 - 500)| / 500 × 100 = 2.4%

Frequently Asked Questions

No, percent error is always reported as a positive value because we use the absolute value of the difference between observed and true values. The direction of error (over or under) can be determined by comparing the observed and true values directly.

An acceptable percent error depends on the field and application:

0-1%: Excellent for precise scientific measurements
1-5%: Good for most laboratory experiments
5-10%: Acceptable for many engineering applications
Over 10%: May indicate measurement problems

Percent error compares a measured value to a known true value, while percent difference compares two experimental values where neither is necessarily "correct." Percent difference is calculated as the difference between two values divided by their average, multiplied by 100%.

Percent Error Calculator