How to Use This Wheelchair Ramp Slope & Length Calculator
Choose inches or centimeters, then enter the total rise: the vertical distance from the ground to the top of the landing or door threshold. Pick a slope (1:12 is the ADA maximum) or type a custom ratio. If you know how much straight-line room you have, enter it and the tool tells you whether the ramp fits and what the gentlest workable slope would be. The results show ramp run, surface length, number of landings, total footprint, and a side-by-side comparison of common slopes.
Why This Matters
Ramp length surprises almost everyone. A single 7-inch front-door step needs about 7 feet of 1:12 ramp. A 30-inch deck needs 30 feet of ramp plus landings, which is longer than most side yards. Discovering that after buying lumber, or after a contractor quote arrives, is expensive and frustrating.
People run these numbers in many situations: a parent coming home from the hospital, an aging relative who wants to stay in the house, a landlord answering an accommodation request, a small business fixing a one-step entrance, or a family adding a ramp for a mobility van. Each case has the same core problem: turn a vertical height into a horizontal distance, and then check whether that distance fits on the property.
The slope matters for people as well as for code. A ramp that technically meets 1:12 can still be exhausting for someone propelling a manual chair alone, which is why many occupational therapists suggest 1:16 or 1:20 when space allows. Planning with real numbers lets you balance comfort, cost, and available space before you build.
How It's Calculated
The geometry is a right triangle. The rise is the vertical side, the run is the horizontal side, and the ramp surface is the hypotenuse.
Surface length = √(Rise² + Run²)
Grade % = 100 ÷ Ratio
Angle = arctan(1 ÷ Ratio)
Sections = Rise ÷ 30 in, rounded up
Footprint = Run + 60 in × Sections
The footprint adds a 60-inch landing at the top and a 60-inch landing between each pair of ramp runs. The calculator rounds lengths up to the next whole inch so you never end up short, and it flags any slope steeper than the 1:12 limit.
The rules of thumb follow the 2010 ADA Standards for Accessible Design, section 405: maximum slope 1:12, maximum 30 inches of rise per run, level landings at least 60 inches long, 36 inches minimum clear width, handrails on both sides when the rise exceeds 6 inches, and edge protection. For one- and two-family homes, IRC R311.8 also uses 1:12 for the required egress ramp. Codes differ by jurisdiction and edition, and this tool is a planning aid. It is not an engineering, permit, or inspection approval.
Worked Example
A porch floor sits 24 inches above the ground, and you want a 1:12 ramp.
- Run: 24 in × 12 = 288 in, which is 24 ft 0 in.
- Surface length: √(24² + 288²) = √83,520 ≈ 288.998, rounded up to 289 in (24 ft 1 in). This is the length of your stringers.
- Grade and angle: 100 ÷ 12 = 8.33%, and arctan(1/12) ≈ 4.76°.
- Sections: 24 ÷ 30 = 0.8, rounded up to 1 section, so no intermediate landing is needed.
- Footprint: 288 in + 60 in top landing = 348 in, or 29 ft 0 in.
- Handrails: the rise is over 6 in, so both sides need them.
If the rise were 40 inches instead, the ramp would need 2 sections of 20 inches each, 480 inches (40 ft) of run, and 60 + 60 inches of landings, for a 50-foot footprint.
Tips & Common Mistakes
- Measure rise to the finished surface. Measure from the ground to the top of the threshold or deck board, not to the framing. Add any planned gravel, pavers, or concrete pad thickness at the bottom.
- Do not forget landings. Many DIY plans include only the sloped run. A 60 by 60 inch top landing is needed so a wheelchair can turn and open the door.
- Treat 1:12 as a maximum, not a target. If you have the room, 1:16 or 1:20 is noticeably easier to climb and safer to descend.
- Short on space? Change the layout. L-shaped or switchback ramps need 60-inch turning landings but fit far more compactly than one straight run. Do not steepen the slope.
- Check local rules before buying materials. Permits, frost-depth footings, guard heights, and surface requirements vary, and a private home may be held to different rules than a public building.
Frequently Asked Questions
What is the maximum slope for a wheelchair ramp?
The ADA maximum is 1:12, meaning 1 inch of rise for every 12 inches of run (8.33% grade). The IRC uses the same 1:12 limit for the required egress ramp at a home. Steeper slopes are allowed only in narrow existing-building exceptions.
How long should a wheelchair ramp be for a 24-inch rise?
At 1:12 the ramp run is 24 feet, plus at least a 5-foot top landing, for about 29 feet total. At the gentler 1:20 slope the run grows to 40 feet.
Does a wheelchair ramp need landings?
Yes. Under ADA rules, a level landing at least 60 inches long is needed at the top and bottom, and at every change of direction. Under ADA 405.6, no single run may rise more than 30 inches without a landing.
Is a 1:12 ramp too steep for a manual wheelchair?
It meets the standard, but many people cannot climb it unassisted, especially on long runs. If the site allows, 1:16 to 1:20 is much easier, and a user or occupational therapist can advise on what works for them.
How wide does a wheelchair ramp need to be?
The ADA requires at least 36 inches of clear width between handrails or curbs. Many builders choose 42 to 48 inches for easier turning and room for a helper walking alongside.
Do I need a permit to build a wheelchair ramp?
Often yes, particularly for ramps attached to a house, those above a set height, or those serving a business. Requirements vary widely, so call your local building department before you begin.