Enter the Rise, then a target Slope or an available Run. You get Run, Ramp Length and Slope at once.
This page's URL keeps these numbers, so someone else opening the link will see the same result.
| 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 |
At 1:12, the run along the ground is 12 times the rise in inches, and the sloped ramp length is a little longer.
| Rise | Run | Ramp length |
|---|---|---|
| 7 in | 84 in (7.0 ft) | 84.29 in (7.0 ft) |
| 12 in | 144 in (12.0 ft) | 144.50 in (12.0 ft) |
| 2 ft (24 in) | 288 in (24.0 ft) | 289.00 in (24.1 ft) |
| 3 ft (36 in) | 432 in (36.0 ft) | 433.50 in (36.1 ft) |
Run is the flat distance along the ground; ramp length is the sloped surface you walk or roll on.
The calculator default, 30 in of rise and 360 in of run, is the same 1:12 math.
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%.
It depends who is using it. A wheelchair ramp on a new build cannot be steeper than 1:12 under the 2010 ADA Standards, so 1:10 is too steep for that job. The same 24 in rise takes 24.0 ft of run at 1:12, and 20.0 ft at 1:10.
A car can take about 15%. 1:10 is gentler than that, so it is not too steep for a driveway. Don't borrow the wheelchair cap for a car, or the other way around.
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.
At 1:12, the run is 12 times the rise and the sloped length is a little longer. The table under How long for a 7 in, 12 in, 2 ft, or 3 ft rise works those four common heights.
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.
