How close was your measurement?
Enter your experimental (measured) value and the theoretical (true) value to see the percent error, the absolute error, and whether you came in over or under the accepted result.
Your values
What this means
Sensitivity around your measurement
| Experimental value | Absolute error | Percent error | Direction |
|---|
Understanding percent error
What Is Percent Error?
Percent error quantifies the accuracy of a measurement by comparing an experimental value to an accepted (actual) value. The formula is |Experimental - Actual| / |Actual| × 100. A smaller percent error indicates a more accurate measurement, while a larger value suggests significant deviation from the expected result.
When to Use Percent Error
Percent error is widely used in science, engineering, and quality control. In chemistry labs, it measures how close an experimental yield is to the theoretical yield. In manufacturing, it assesses product tolerance. In physics, it evaluates the precision of experimental measurements against known constants.
Percent Error vs Percent Difference
Percent error compares a measured value to a known standard. Percent difference compares two measured values when neither is considered the "correct" one. The formulas differ: percent difference uses the average of the two values as the denominator rather than one accepted value.
Reducing Measurement Error
To minimize percent error, calibrate instruments before use, take multiple measurements and average them, control environmental variables, and use appropriate precision tools. Systematic errors can be identified and corrected, while random errors are reduced by increasing sample size.
Common questions
Can percent error be negative?
The standard formula uses absolute value, so percent error is always positive. However, some contexts report signed error to show whether the measurement was above (+) or below (-) the actual value.
What is a good percent error?
It depends on the field. In chemistry, under 5% is generally acceptable. In physics, under 1% may be expected. In manufacturing, tolerances vary by product specifications.
What if the actual value is zero?
Percent error is undefined when the actual value is zero because you cannot divide by zero. In such cases, use absolute error instead.
How is percent error different from absolute error?
Absolute error is simply |Experimental - Actual| without dividing by the actual value. Percent error expresses that difference as a percentage of the actual value, making it easier to compare across different scales.
Estimates only. Percent error is undefined when the true value is zero; use absolute error in that case.