Percentage Error Calculator
Calculate percentage, absolute, and relative error
About the Percentage Error Calculator
Percentage error tells you how far off a measurement or estimate is from the true value, as a proportion — the standard way to express accuracy in science and engineering. This calculator takes the exact value and the approximate value and returns the percentage error, along with the absolute and relative error behind it.
Students use it to grade the accuracy of lab measurements; anyone comparing an estimate to a known figure uses it to quantify how close they got. By breaking out absolute and relative error too, it shows the full chain from raw difference to final percentage, and it handles the awkward case where the exact value is zero gracefully.
How to Use the Percentage Error Calculator
- Enter the exact (true) value.
- Enter the approximate (measured or estimated) value.
- Read the percentage error.
- Review the absolute error and relative error shown in the step-by-step breakdown.
Why Use ToolForge’s Percentage Error Calculator
- It reports all three related figures — percentage error, absolute error, and relative error — so you see how the final percentage is derived.
- It uses the standard formula, taking the absolute difference over the true value, so signs never distort the result.
- It handles a zero exact value gracefully, showing the absolute error rather than producing a division error.
- Calculations are instant and run locally with no account.
Frequently Asked Questions
How is percentage error calculated?
It is the absolute difference between the approximate and exact values, divided by the absolute exact value, multiplied by 100. For an exact value of 100 and an approximate of 95, the percentage error is |95−100| ÷ 100 × 100 = 5%.
What is the difference between absolute and relative error?
Absolute error is the raw difference between the measured and true values, in the original units. Relative error is that difference divided by the true value, a unitless ratio. Percentage error is simply the relative error expressed as a percentage.
Why can't I use an exact value of zero?
Percentage and relative error require dividing by the exact value, and division by zero is undefined. When the exact value is zero, this calculator shows the absolute error instead, since a meaningful percentage cannot be computed.
What counts as a good percentage error?
It depends entirely on context — a low percentage error means the approximation is close to the true value. Many school labs treat under 5% as good, but precision fields demand far smaller errors, while rough estimates may tolerate more. Lower is always better.
