Enter the Rise, then a target Slope or an available Run. You get Run, Ramp Length and Slope at once.
| Slope | Run (in) | Ramp Length (in) |
|---|---|---|
| 1:12 | 360.00 | 361.25 |
| 1:16 | 480.00 | 480.94 |
| 1:20 | 600.00 | 600.75 |
| 2:12 residential | 180.00 | 182.48 |
| 3:12 loading | 120.00 | 123.69 |
Find your situation in the table, then read its block below for a worked example. Every slope is shown three ways that mean the same thing: as a ratio, a percent grade and an angle.
| Use case | Ratio | Percent grade | Angle |
|---|---|---|---|
| Wheelchair & accessibility ramps | 1:12 | 8.3% | 4.76° |
| Car & vehicle ramps | 1:6.67 | 15% | 8.53° |
| Shed & deck ramps | 1:4 | 25% | 14.04° |
| Trailer & loading ramps | 1:5 | 20% | 11.31° |
| Dog & pet ramps | 1:2.75 | 36.4% | 20° |
| Boat ramps | 1:7.69 | 13% | 7.41° |
1:12 maximum (1:16 for a comfortable self-push)
Example: a 24 in rise needs about a 24.0 ft run and a 24.1 ft ramp length.
The 2010 ADA standard caps a new ramp at 1:12, the steepest a person can safely self-propel; handrails are required once the rise is over 6 in.
up to about 15% (1:6.7)
Example: a 18 in rise needs about a 10.0 ft run and a 10.1 ft ramp length.
A low front bumper or spoiler scrapes on anything steeper, so ~15% is the practical ceiling for a driveway or service ramp.
around 3:12 (25%) or gentler
Example: a 12 in rise needs about a 4.0 ft run and a 4.1 ft ramp length.
Past ~25% a loaded wheelbarrow, mower or hand truck gets hard to control on the way down, so 3:12 is the working limit.
about 1:5 (20%), gentler for low clearance
Example: a 15 in rise needs about a 6.3 ft run and a 6.4 ft ramp length.
A long wheelbase with low ground clearance grounds out on the break-over angle, so the ramp must stay long and gentle enough for the chassis to clear the joint.
a gentle 18–22° (drop lower for senior dogs)
Example: a 12 in rise needs about a 2.8 ft run and a 2.9 ft ramp length.
Steeper than ~22° and most dogs balk or slip; senior dogs and any with hip or joint trouble need it shallower still.
12–15% (about 1:8 to 1:7) at the launch
Example: a 13 in rise needs about a 8.3 ft run and a 8.4 ft ramp length.
It has to be deep enough to float the hull yet flat enough that the tow vehicle keeps traction on a wet, often slick surface. The usable band is 12–15%.
The table gives you a target, but the slope you can actually build is whatever your space allows. Work through it in four steps:
That chain (rise → acceptable slope → required run and length → adjust for the space) is all there is to it. The numbers above are starting points; your measured rise and available run decide the rest.
Every ramp is a right triangle. The rise is the vertical height, the run is the horizontal distance along the ground, and the ramp length is the sloped side connecting them.
Slope is one idea with three interchangeable forms:
They all describe the same steepness, which is why a 100% grade equals 45° (the rise equals the run), and 1:12 equals 8.3% equals 4.76°. Cross-slope (the sideways tilt added for drainage) is a separate measurement, capped at 1:48 under the 2010 ADA standard.
Slope is rise divided by run. A 30 in rise over a 360 in run is 30 ÷ 360 = 1:12 = 8.3%.
Gradient (percent grade) is rise ÷ run × 100. The same 1:12 ramp works out to 8.3%.
Ramp length is the sloped surface, the hypotenuse: length = √(rise² + run²). It is always a little longer than the run.
Rise is the vertical height the ramp climbs; run is the horizontal distance it covers along the ground. Slope is simply rise over run.
Run is measured flat along the ground; ramp length is measured up the slope itself. The steeper the ramp, the bigger the gap between them.
