How long does a ramp need to be?

Multiply the rise by the slope ratio. At the 1:12 wheelchair maximum, every inch of rise needs 12 inches of run, so a deck 24 in above the ground needs a ramp 24 ft long, plus landings. At 1:20 the same deck needs 40 ft. A 1:8 ramp is only 16 ft but is too steep for most wheelchair users.

What is the code for a ramp at a house?

The IRC (R311.8) limits the ramp that serves the required exit door to 1:12 and other ramps to 1:8, requires a 3 ft by 3 ft landing at the top and bottom, where a door opens onto the ramp and where it turns, and requires a handrail on at least one side when the ramp is steeper than 1:12. Local amendments can be stricter.

How many feet of ramp do I need for 3 steps?

Three steps at about 7 in each is roughly 21 in of rise, so a 1:12 ramp needs about 21 ft of run. Under the ADA rules that is still one run, because each run may climb up to 30 in before it needs a 60 in landing.

When does a ramp need handrails?

Under the ADA Standards, any ramp run that rises more than 6 in needs handrails on both sides, 34 to 38 in high. Under the IRC, a house ramp needs a handrail on at least one side once it is steeper than 1:12. Any open side more than 30 in above the ground also needs a guard.

How wide should a deck ramp be?

The ADA Standards require at least 36 in clear between the handrails, so frame the ramp about 42 to 48 in wide to leave room for posts and rails. The IRC sets no ramp width for houses, but 36 in clear is the practical minimum for a wheelchair.

Stairs & Railings

Deck Ramp Calculator

A ramp is a long, shallow stair: every inch of rise needs a set length of run, so the height of the deck decides how long the ramp is. This works out the run for the slope you choose, the landings the code asks for, the sloped length you frame and deck, how many stringers the width takes and whether handrails are required — under the house code (IRC R311.8) or the stricter ADA Standards for an accessible route.

How long a ramp has to be

Ramp length is the rise times the slope ratio. A 1:12 slope, the maximum for wheelchair use in both the IRC (for the ramp serving the exit door, R311.8.1) and the ADA Standards (405.2), needs 12 inches of run for every inch the deck sits above the ground.

Rise	1:8	1:12	1:16	1:20
12 in	8 ft	12 ft	16 ft	20 ft
18 in	12 ft	18 ft	24 ft	30 ft
24 in	16 ft	24 ft	32 ft	40 ft
30 in	20 ft	30 ft	40 ft	50 ft
36 in	24 ft	36 ft	48 ft	60 ft

Worked example: a deck 24 in above the yard

Step	Working	Result
Run at 1:12	24 in × 12	288 in = 24 ft
Sloped length	√(288² + 24²)	289 in = 24 ft 1 in
Stringers, 48 in wide at 16 in on centre	48 ÷ 16 + 1	4 stringers
Decking	289 in × 48 in ÷ 144	96 sq ft
IRC landing	R311.8.2	3 ft × 3 ft at the bottom; the deck is the top
Handrail (IRC)	R311.8.3: only steeper than 1:12	Not required

Under the ADA Standards the same ramp is still one run, because 24 in is under the 30 in limit per run (405.6), but it needs 60 in landings top and bottom (405.7.3) and handrails on both sides because it rises more than 6 in (405.8). A deck 36 in up would need two runs of 18 ft with a 5 ft landing between them.

Building it

Stringers. Rip 2x10 or 2x12 stringers to the slope, or frame level joists on posts that step down; keep them at 16 in on centre like deck joists (DCA 6).
Surface. Run the boards across the slope so wheels roll over the gaps, and pick a textured board; wet smooth composite is slippery on a slope.
Bottom. Finish on a firm, level landing — a concrete pad or compacted gravel — so the ramp does not end in mud.
Edges. Add a curb or rail near the surface on open sides so a wheel cannot drop off (ADA 405.9).

Handrails for the ramp follow the same rules as stairs — size them with the stair handrail calculator. If a ramp is too long for the yard, the stair stringer calculator lays out steps instead, and the deck railing calculator prices the guards along the open sides.

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Frequently asked questions

How long does a ramp need to be?: Multiply the rise by the slope ratio. At the 1:12 wheelchair maximum, every inch of rise needs 12 inches of run, so a deck 24 in above the ground needs a ramp 24 ft long, plus landings. At 1:20 the same deck needs 40 ft. A 1:8 ramp is only 16 ft but is too steep for most wheelchair users.
What is the code for a ramp at a house?: The IRC (R311.8) limits the ramp that serves the required exit door to 1:12 and other ramps to 1:8, requires a 3 ft by 3 ft landing at the top and bottom, where a door opens onto the ramp and where it turns, and requires a handrail on at least one side when the ramp is steeper than 1:12. Local amendments can be stricter.
How many feet of ramp do I need for 3 steps?: Three steps at about 7 in each is roughly 21 in of rise, so a 1:12 ramp needs about 21 ft of run. Under the ADA rules that is still one run, because each run may climb up to 30 in before it needs a 60 in landing.
When does a ramp need handrails?: Under the ADA Standards, any ramp run that rises more than 6 in needs handrails on both sides, 34 to 38 in high. Under the IRC, a house ramp needs a handrail on at least one side once it is steeper than 1:12. Any open side more than 30 in above the ground also needs a guard.
How wide should a deck ramp be?: The ADA Standards require at least 36 in clear between the handrails, so frame the ramp about 42 to 48 in wide to leave room for posts and rails. The IRC sets no ramp width for houses, but 36 in clear is the practical minimum for a wheelchair.