Eighteen inches: a long straight ramp or a turn
An 18 inch rise needs 18 ft of ramp, and 23 ft from the door once the 5 ft top landing is added. Many front yards do not have that much room in a straight line, so ramps of this height are often turned at a landing and brought back alongside the house.
The rise is under 30 inches, so the rules do not force a landing part way: any landing you add is for the turn. Each landing is at least 60 inches long, so a turn adds 5 ft of level platform to the 18 ft of sloping ramp.
18 inch rise at each slope
| Slope | Ramp length (run) | Along the surface | Percent | Angle | Runs | Footprint with landings |
|---|---|---|---|---|---|---|
| 1:12 (ADA maximum) | 18 ft | 18.06 ft | 8.3% | 4.8° | 1 | 23 ft |
| 1:16 | 24 ft | 24.05 ft | 6.3% | 3.6° | 1 | 29 ft |
| 1:20 | 30 ft | 30.04 ft | 5.0% | 2.9° | 1 | 35 ft |
The footprint adds a 5 ft landing at the top. Allow 5 ft of clear, level space at the bottom too: with it the 1:12 ramp needs 28 ft from end to end. That bottom space is not in the concrete estimate below.
Is my ramp too steep for 18 inches?
Slope is rise ÷ run. For an 18 inch rise, a ramp shorter than 18 ft is steeper than 1:12:
| Ramp length | Slope | Percent | Angle | Within 1:12? |
|---|---|---|---|---|
| 14 ft | 1:9.3 | 10.7% | 6.1° | No, 4 ft too short |
| 16 ft | 1:10.7 | 9.4% | 5.4° | No, 2 ft too short |
| 18 ft | 1:12 | 8.3% | 4.8° | Yes |
| 22 ft | 1:14.7 | 6.8% | 3.9° | Yes |
Materials for the 18 ft ramp
A wood ramp 18 ft long and 36 inches wide takes 39 rows of 5/4×6 deck boards laid across it, 129 lineal feet with 10% extra, on 4 joists per run at 16 inch centers (80 lineal feet). The 4 inch concrete for the top landing is 0.34 cubic yards, about 16 bags of 80 lb mix. Built 48 inches wide, the decking rises to 172 lineal feet on the same 4 joists per run. Handrails on both sides, with a 12 inch level extension at the top and bottom of the run, come to 41 lineal feet of rail. Posts, brackets and footings are not in these figures.
Ramp length for nearby rises
| Rise | 1:12 | 1:16 | 1:20 | Runs | Footprint at 1:12 |
|---|---|---|---|---|---|
| 14 in | 14 ft | 18.67 ft | 23.33 ft | 1 | 19 ft |
| 16 in | 16 ft | 21.33 ft | 26.67 ft | 1 | 21 ft |
| 18 in | 18 ft | 24 ft | 30 ft | 1 | 23 ft |
| 20 in | 20 ft | 26.67 ft | 33.33 ft | 1 | 25 ft |
| 22 in | 22 ft | 29.33 ft | 36.67 ft | 1 | 27 ft |
Coming down steps instead of a measured height? See a ramp for 2 steps or a ramp for 3 steps, or read the ramp length and slope guide.
Want to change anything else? The calculator above is the full Wheelchair Ramp Calculator: edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How long does a wheelchair ramp need to be for an 18 inch rise?
18 ft at the 1:12 maximum slope, because every inch of rise needs 12 inches of ramp. With the landings it takes up 23 ft. At 1:16 the ramp is 24 ft and at 1:20 it is 30 ft.
Can an 18 inch rise be done in one ramp run?
Yes. One run may climb up to 30 inches, so an 18 inch rise is a single 18 ft run at 1:12 with a landing at the top. A landing part way up is only needed if the ramp changes direction.
What is the slope of an 18 ft ramp with an 18 inch rise?
1:12, which is 8.3% or 4.8 degrees. Divide the rise by the run in the same unit: 18 ÷ 216 inches = 0.0833.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.