Ramp Slope Calculator
Convert a ramp's rise and run into a gradient ratio (1 in x), a percentage and an angle, and check it against the common accessibility limits.
How steep the ramp is, and whether it meets the usual limit.
How the ramp slope calculator works
A ramp's gradient is its rise over its run, usually written as a ratio: 1 in 12 means 1 unit of rise for every 12 of run (8.3%, 4.8°). Accessibility rules cap ramps: 1 in 12 is the maximum many codes allow for wheelchair access, 1 in 14 is the maximum in some, and 1 in 20 is gentle enough to need no handrails in most. The calculator gives the ratio, percentage and angle and, in Detailed mode, the run needed to reach a chosen gradient.
Long ramps also need landings at intervals; check the code that applies.
Formula: ratio = run ÷ rise · slope % = rise ÷ run × 100 · angle = arctan(rise ÷ run)
Worked examples
| Inputs | Gradient | Note |
|---|---|---|
| 500 mm rise over 6 m | 1 in 12 | 1 in 12 — 8.3% |
| 500 mm rise over 7 m | 1 in 14 | 1 in 14 |
| 20 in rise over 20 ft | 1 in 12 | 1 in 12 |
FAQFrequently asked questions
What is the maximum slope for a wheelchair ramp?
Commonly 1 in 12 (8.3%), with some codes requiring 1 in 14 for public buildings and gentler gradients for longer ramps. Check the standard that applies where you build.
How long must a ramp be for a 500 mm rise?
At 1 in 14, 7 m of run; at 1 in 12, 6 m. Add landings — most codes require one every 9 m or so of ramp and at every change of direction.
How do ratio, percentage and degrees relate?
1 in 12 = 8.33% = 4.76°. Percentage is rise ÷ run × 100; degrees is the arctangent of rise ÷ run.
Do I need handrails?
Usually on any ramp steeper than 1 in 20 or with a rise over about 150 mm, on both sides. The applicable code specifies heights and extensions.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Cement Concrete & Aggregates Australia — concrete basics and yields — bag yields, density 2,400 kg/m³
- Australian Building Codes Board — the National Construction Code
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.