Ramp Calculator
Find how long a ramp has to be. Enter the total rise in inches, pick a slope ratio (1:12 ADA maximum, gentler 1:16 or 1:20, or 1:8 for limited existing-site cases), and get ramp length in feet and inches, the angle, and the grade.
Example: with Total rise (inches) 24 · Slope ratio 1:12 — ADA maximum for new construction → Ramp length needed: 24 ft (288 in of run).
- Incline angle4.76°
- Grade8.33%
- ADA noteSlope meets ADA; single run OK (30 in max rise between landings)
Computed by the calculator below using its default values. Change any input to see your own numbers.
The ADA maximum slope is 1:12 — one foot of ramp for every inch of rise. A 24-inch porch needs 24 feet of ramp, plus landings.
The 1:12 rule and what it costs in length
ADA's ramp limit for new construction is a 1:12 slope — every inch of vertical rise demands at least 12 inches of ramp run. The convenient version: one foot of ramp per inch of rise. A typical 24-inch porch rise therefore needs 24 feet of ramp, which surprises most first-time builders and is why wraparound and switchback layouts exist. Gentler slopes of 1:16 or 1:20 are meaningfully easier for someone self-propelling a manual chair, at the cost of yet more length.
Slope is only part of compliance. ADA also caps any single run at 30 inches of rise, requires 60-inch level landings at top, bottom, and between runs, a 36-inch minimum clear width, and handrails on runs rising more than 6 inches.
Home ramps and steeper slopes
Private homes are not bound by ADA, but the standard exists because steeper ramps genuinely stop being usable: at 1:8 (7.1°) many manual wheelchair users cannot ascend safely, and descending gets hazardous. Reserve steep ratios for short rises, occupied-assist situations, or portable ramps rated for them, and treat 1:12 as the practical ceiling for independent use. Local building codes may add their own requirements — check before you build.
How it’s calculated
Ramp run (in) = rise (in) × slope ratio, shown in feet at 12 in/ft. Angle = arctan(1 ÷ ratio); grade % = 100 ÷ ratio. ADA notes follow the 2010 ADA Standards, section 405: 1:12 max slope for new construction, 30 in max rise per run, landings between runs.
Length shown is sloped run only — add 60-inch level landings at top and bottom (and at every 30 in of rise) for a compliant, usable layout.
Ramp slopes compared
| Slope | Ramp per inch of rise | Angle | Grade | Use |
|---|---|---|---|---|
| 1:8 | 0.67 ft | 7.13° | 12.5% | Existing sites only, ≤ 3 in rise |
| 1:12 | 1.00 ft | 4.76° | 8.3% | ADA max, new construction |
| 1:16 | 1.33 ft | 3.58° | 6.25% | Easier manual propulsion |
| 1:20 | 1.67 ft | 2.86° | 5.0% | Below ADA ramp threshold |
Slope limits from 2010 ADA Standards §405; angles computed as arctan(1/ratio).
Common mistakes
- Measuring rise from the ground to the door sill but forgetting the landing or threshold height at the top.
- Counting landings as part of the sloped run — the 24 ft of ramp is in addition to level landings.
- Building 2:12 'to save space' for a manual wheelchair user, which many cannot climb and few can descend safely.
- Ignoring cross slope: ADA caps side-to-side slope at 1:48, and a tilted ramp is worse than a slightly steep one.
Frequently asked questions
What is the ramp length formula?
Ramp run = rise × slope ratio. At the ADA 1:12 slope that means 1 foot of ramp per inch of rise: a 20-inch rise needs 20 feet of ramp, plus level landings at each end.
How long a ramp do I need for 3 steps?
Three typical 7.5-inch steps is about 22.5 inches of rise, so roughly 22.5 feet of ramp at 1:12. You would also need a landing at the door and one at the bottom.
Does ADA apply to my house?
No — ADA governs public accommodations and commercial facilities. But its 1:12 limit is still the right design guideline at home, because it reflects what wheelchair users can actually negotiate. Local residential codes may impose their own rules.
What is the maximum rise for one ramp run?
30 inches under ADA. Past that you must break the ramp with an intermediate 60-inch level landing before continuing, which adds real length to tall porches — a 36-inch rise is two runs plus three landings.