How Long a Wheelchair Ramp for 20 Inches of Rise?

A 20 inch rise needs a 20 ft wheelchair ramp at 1:12, the steepest slope the ADA allows: 1 foot of ramp for every inch of rise. It is built as one run, with no landing part way up, and takes up 25 ft with the 5 ft landing at the top. At 1:16 the ramp is 26.67 ft, and at 1:20 it is 33.33 ft.

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Example job shown. Change the numbers to match yours.

Ramp length (horizontal run)

20.0 ft

1 inch of rise needs 12 inches of ramp. Measure this along the ground, not along the sloping surface

What to buy

Decking, with 10% extra142 lineal ft of boards, rounded up
Joists per run (16 in centers)4 joists
Joist lumber (size from a span table), with 10% extra89 lineal ft of lumber, rounded up
80 lb bags of concrete mix for those landings (0.6 ft³ each)16 bags

Walking surface length (along the slope): 20.1 ft
Separate ramp runsEach run climbs no more than 30 in: 1 run
Intermediate landings (5 × 5 ft): 0 landings
Landings in total (5 ft × 5 ft clear space at each)1 top + 0 intermediate + 1 clear space at the bottom. The concrete and bag counts below cover the top and intermediate landing (1), not the bottom one: 2 landings
Total footprint with a 5 ft top landing: 25.0 ft
Footprint with the 5 ft clear space at the bottom as wellThe bottom 5 ft is level ground or a landing you pour or lay separately: it is not in the concrete below: 30.0 ft

Materials (wood ramp runs, concrete landings)

Deck boards (5/4×6, laid across the ramp)Each row is one board 3.0 ft long: 43 board rows
Concrete for the top landing (1 at 5 ft × 5.0 ft, 4 in thick, +10%): 9.2 ft³
Same concrete in cubic yards: 0.34 yd³

Requirements to check

Handrails needed (rise over 6 in): Yes, both sides
Handrail length, both sides, with 12 in extensionsEach side: the walking surface length plus 12 in at the top and bottom of every run (ADA Standards 405.8 and 505.10.1). Rail stock, posts and brackets are extra: 45 lineal ft
Clear width: 36 in

Size the joists for their span from a span table or your plans examiner.
Under the ADA, the maximum slope is 1:12, the maximum rise of one run is 30 inches, landings must be at least 60 inches long and as wide as the ramp, and the clear width must be at least 36 inches. Residential rules differ by place, so check local codes, and allow 5 ft of clear space at the bottom. The materials list is a planning estimate for a wood-framed ramp with a concrete top landing and any intermediate landings: the concrete covers the top and intermediate landings only, not the level 5 ft at the bottom. It leaves out posts, footings and guards (the handrail length is given above), whose spacing and size depend on your loads, frost depth and local code.

Before you buy: round up to whole packs, check the size printed on the label, and add a little spare. Your supplier has the final say.

Blueprint

20 ft ramp

Twenty inches: what the frame and rails take

A 20 inch rise is a 20 ft ramp in one run, and at that length the lumber is worth pricing before you start. The sloping surface is 20.07 ft, which is 43 rows of deck boards on 4 joists the full length of the run.

The rails are the other long item: 45 lineal feet for both sides, including the 12 inch extensions. At 1:16 the same rise is 26.67 ft of ramp and the rail grows to 58 lineal feet.

20 inch rise at each slope

Slope	Ramp length (run)	Along the surface	Percent	Angle	Runs	Footprint with landings
1:12 (ADA maximum)	20 ft	20.07 ft	8.3%	4.8°	1	25 ft
1:16	26.67 ft	26.72 ft	6.2%	3.6°	1	31.67 ft
1:20	33.33 ft	33.37 ft	5.0%	2.9°	1	38.33 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 30 ft from end to end. That bottom space is not in the concrete estimate below.

Is my ramp too steep for 20 inches?

Slope is rise ÷ run. For a 20 inch rise, a ramp shorter than 20 ft is steeper than 1:12:

Ramp length	Slope	Percent	Angle	Within 1:12?
16 ft	1:9.6	10.4%	5.9°	No, 4 ft too short
18 ft	1:10.8	9.3%	5.3°	No, 2 ft too short
20 ft	1:12	8.3%	4.8°	Yes
24 ft	1:14.4	6.9%	4.0°	Yes

Materials for the 20 ft ramp

A wood ramp 20 ft long and 36 inches wide takes 43 rows of 5/4×6 deck boards laid across it, 142 lineal feet with 10% extra, on 4 joists per run at 16 inch centers (89 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 190 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 45 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
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
24 in	24 ft	32 ft	40 ft	1	29 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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Portable folding ramp

Frequently asked questions

How long does a wheelchair ramp need to be for a 20 inch rise?

20 ft at the 1:12 maximum slope, because every inch of rise needs 12 inches of ramp. With the landings it takes up 25 ft. At 1:16 the ramp is 26.67 ft and at 1:20 it is 33.33 ft.

How much handrail does a 20 foot ramp need?

45 lineal feet for both sides of a ramp with a 20 inch rise: each side is the 20.07 ft walking surface plus 12 inches level at the top and at the bottom. Posts and brackets are extra.

What is the slope of a 20 ft ramp with a 20 inch rise?

1:12, which is 8.3% or 4.8 degrees. Divide the rise by the run in the same unit: 20 ÷ 240 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.

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