Comprehensive Calculator Guide
Percent error measures how far a measured value is from the true value, relative to the true value: |measured − true| ÷ |true| × 100. A student who measures gravity as 9.6 m/s² against the accepted 9.81 has a 2.14% error. Enter both values to get the percent and absolute error.
Absolute and percent error
The absolute error is the gap without sign: |9.6 − 9.81| = 0.21. On its own it says little, since 0.21 matters far more against 9.81 than against 1,000. Dividing by the true value and multiplying by 100 gives the percent error, which lets you compare experiments in different units.
The absolute value makes the result positive whichever side you missed on. If you want to see a consistent bias, compute the signed difference yourself. What counts as acceptable depends on the field: under 5% is often fine in school labs, far less in industry.
How to Use
- 01Enter your measured value.
- 02Enter the true or accepted value, in the same unit.
- 03Read the percent error and absolute error.
Formula Used
Percent error = |measured − true| ÷ |true| × 100Practical Examples
Example 1: gravity
9.6 against 9.81 m/s²: absolute error 0.21, percent error 2.14%.
Example 2: a scale
52 g on a scale for a 50 g sample: 4%.
Example 3: boiling point
98.5 °C against 100 °C: 1.5%.
Important Tips
- Average repeated measurements before computing the error.
- Report the error with its likely causes.
Common Mistakes to Avoid
- Dividing by the measured value instead of the true one.
- Forgetting to multiply by 100.
Frequently Asked Questions
- How do I calculate percent error?
- Take the absolute difference, divide by the true value and multiply by 100.
- Can percent error be negative?
- Not with the usual absolute-value formula.
- How is it different from percentage difference?
- Percent error compares against a known true value; percentage difference compares two values relative to their average.
- Why can't the true value be zero?
- You cannot divide by zero; use the absolute error instead.