Experimental data & uncertainty · SL/HL
Percentage uncertainty
Express an absolute uncertainty as a percentage.
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Number formats & units
Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.
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Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| Absolute uncertainty in the same unit as x. |
Worked example
- Measured value x
- 25.00
- Absolute uncertainty Δx
- 0.05
- Result unit (optional)
- cm³
- Uncertainty significant figures
- 1 significant figure
(25.00 ± 0.05) cm³
Follow the example steps
- Percentage uncertainty = Δx/|x| × 100
- = 0.05 / |25| × 100 = 0.2%
- Rounded measurement: (25.00 ± 0.05) cm³
Common mistakes
Use matching units for the value and its absolute uncertainty.
Incorrect approach
x = 10 cm, Δx = 1 mm: 100 × 1/10 = 10%
Correct approach
Δx = 0.1 cm: 100 × 0.1/10 = 1%
More checks before you submit
- Convert value and uncertainty to the same unit first.
Method notes
Percentage uncertainty lets you compare the relative size of uncertainty across measurements.