Slope & Grade Formula
Ratio: 1 : (Run ÷ Rise)
Angle: atan(Rise ÷ Run) × 180 ÷ π
Fall per Metre: (Rise ÷ Run) × 1000 mm/m
Note: Common drainage slopes: 1:60 (1.67%) for stormwater, 1:80 (1.25%) for paved areas, 1:100 (1%) minimum for flat roofs.
Slope & Grade Calculator: Rise, Run & Percentage
From driveway gradients (max 1:4 under most councils) to wheelchair ramps (max 1:14 per AS 1428.1), slope calculations are essential in Australian construction. This converts between percentage grade, ratio, degrees, rise, and run.
Common Slopes in Australian Construction
| Application | Ratio | % | Degrees |
|---|---|---|---|
| Wheelchair ramp (AS 1428.1) | 1:14 | 7.1% | 4.1° |
| Driveway (typical max) | 1:4 | 25% | 14° |
| Floor drainage | 1:100 | 1% | 0.6° |
| Standard roof pitch | 1:2.7 | 36% | 20° |
| Site drainage (min) | 1:50 | 2% | 1.1° |
Formulas
- % = (Rise/Run) × 100
- Degrees = arctan(Rise/Run)
- Ratio = 1 : (Run/Rise)
Frequently Asked Questions
Max driveway gradient in Australia?
Most councils allow 1:4 (25%). Some restrict to 1:5 (20%). Boundary crossings often limited to 1:8.
Slope vs grade vs gradient?
All describe steepness. Grade = percentage. Slope = degrees. Gradient = ratio. All interconvertible.
Wheelchair ramp gradient?
Max 1:14 (7.1%) per AS 1428.1. Landings every 9m, min 1200mm long. Handrails both sides.
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