Calculating your percent error is straightforward once you know the Percent Error formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Percent Error Calculator.
What is Percent Error?
The Percent Error calculation tells you your percent error from a few simple inputs. The figure you are solving for here is the percent error, expressed in percent.
The Percent Error formula
This calculation combines several inputs through a multi-step method rather than a single one-line formula. Enter the values below and the calculator resolves each step in order. The inputs it needs are:
- Measured / experimental value — a number. Example: 98.
- True / theoretical value — a number. Example: 100.
How to calculate it step by step
- Write down the measured / experimental value (for example, 98).
- Write down the true / theoretical value (for example, 100).
- Apply the formula above to get your percent error.
- Double-check the result with the Percent Error Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Measured / experimental value | 98 |
| True / theoretical value | 100 |
| Percent error | 2.000% |
| Absolute error | 2.0000 |
With measured / experimental value of 98 and true / theoretical value of 100, the percent error works out to 2.000%.
Example 2
With measured / experimental value of 200 and true / theoretical value of 100, the percent error works out to 100.000%.
| Result | Value |
|---|---|
| Percent error | 100.000% |
| Absolute error | 100.0000 |
Example 3
With measured / experimental value of 49 and true / theoretical value of 100, the percent error works out to 51.000%.
| Result | Value |
|---|---|
| Percent error | 51.000% |
| Absolute error | 51.0000 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Percent Error Calculator does it instantly, for free, with the formula and a worked example built in.
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