Guide
How to use ADA Ramp Calculator
Start with the working tool above. The notes below explain the inputs, method, limitations and checks that matter for this specific task.
- 1. Pick Design to size a new ramp, or Check to test an existing one.
- 2. Design mode: enter the rise in inches to get the minimum run, percent and angle.
- 3. Read the runs-and-landings result: rises over 30 inches split into runs with landings between.
- 4. Check mode: enter rise and measured run to see the ratio and the 1:12 verdict.
- 5. Confirm width, cross slope and handrails below.
How it works
Section 405 of the 2010 ADA Standards sets these numbers. Running slope (§405.2) may not exceed 1:12 — 12 inches of run per inch of rise (8.33%, about 4.76°). Maximum rise per run (§405.6) is 30 inches, so minimum run = rise × 12; runs needed = rise ÷ 30, rounded up. Landings (§405.7) are required at the top and bottom of each run and at direction changes: 60 inches long minimum, 60 × 60 inches at turns. Cross slope (§405.3) may not exceed 1:48; clear width (§405.5) is at least 36 inches; handrails both sides (§405.8) are required when a run rises over 6 inches. Design mode applies these limits; Check mode compares run ÷ rise with 12.
Worked examples
30 inch rise — maximum for one run
Minimum run = 30 × 12 = 360 inches = 30 feet. Slope = 1 ÷ 12 = 8.33%. Angle = arctan(1 ÷ 12) = 4.76°. At the limit, one run suffices, with 60-inch landings at top and bottom.
12 inch rise at an entrance
Minimum run = 12 × 12 = 144 inches = 12 feet, at 8.33% and 4.76°. Above a 6 inch rise, handrails are required on both sides, with 36 inches clear width.
Checking an existing ramp: 9 inch rise, 96 inch run
Ratio = 96 ÷ 9 = 10.67 (1:10.67) — steeper than 1:12, so it fails as new construction.
When this tool is useful
- Planning an accessible entrance for a shop or office
- Checking whether an existing ramp meets the 1:12 maximum slope
- Preparing measurements before an accessibility review
Key requirements from the 2010 ADA Standards (§405)
The limits used here, from the U.S. Access Board and ada.gov.
| Requirement | Limit | Section |
|---|---|---|
| Running slope | 1:12 maximum | 405.2 |
| Rise per run | 30 in maximum | 405.6 |
| Cross slope | 1:48 maximum | 405.3 |
| Clear width | 36 in minimum | 405.5 |
| Landing length | 60 in minimum | 405.7 |
| Handrails | Both sides when rise > 6 in | 405.8 |
Landings, runs and switchbacks
The 30-inch rise limit makes real ramps long. A 48-inch rise needs two runs (30 and 18 inches) plus bottom, middle and top landings: 576 inches of run plus at least 180 inches of landings, roughly 63 feet straight. A switchback folds it back on itself, with a 60 × 60 inch landing at the turn.
Exceptions for existing facilities (Table 405.2)
Where space makes 1:12 technically infeasible in an existing site, Table 405.2 permits limited steeper slopes for very small rises.
- Up to 1:10 for a maximum rise of 6 inches.
- Up to 1:8 for a maximum rise of 3 inches.
- Steeper than 1:8 is prohibited in all cases.
- Document why 1:12 was infeasible.
Common mistakes to avoid
- Designing to exactly 1:12 with no margin for construction tolerance.
- Forgetting landings: a 36 inch rise needs two runs plus three 60-inch landings.
- Measuring the run along the sloped surface instead of horizontally.
- Ignoring cross slope: a 1:12 ramp fails if it tilts sideways more than 1:48.
- Assuming existing-site exceptions apply to new construction.
Frequently asked questions
What is the maximum slope for an ADA ramp?
No steeper than 1:12 — one inch of rise per 12 inches of run, equal to 8.33% or about 4.76 degrees (§405.2). Steeper slopes appear only in exceptions for existing facilities.
How long must a ramp be for a 24 inch rise?
At 1:12 the run alone is 24 × 12 = 288 inches, or 24 feet. Add 60-inch landings at top and bottom and a straight layout needs roughly 34 feet; a switchback folds it into less space.
When are handrails required on a ramp?
On both sides of a run whose rise exceeds 6 inches (§405.8). They must be continuous and meet the grip, height and extension rules of §505. Smaller rises are exempt.
What are the exceptions for existing buildings?
Table 405.2 allows steeper slopes only where 1:12 is technically infeasible in an existing site: up to 1:10 for a rise of at most 6 inches, up to 1:8 for at most 3 inches. Steeper than 1:8 is never permitted.
How wide does an ADA ramp need to be?
Clear width between handrails: at least 36 inches (§405.5). Landings must be at least as wide as the incoming run, at least 60 inches long, and 60 × 60 inches at turns.
Does this calculator guarantee my ramp is compliant?
No. It applies the headline §405 slope, rise and landing rules, but compliance also covers surfaces, edge protection, handrail geometry, door clearances and stricter local codes. Have the final design reviewed locally.
Bottom line
Multiply the rise by 12 for the minimum run, split the climb into runs of at most 30 inches, and budget 60 inches of landing at every break.
If the question changes shape, the closest neighbours are Driveway Slope Calculator and Triangle Calculator — or browse everything under Construction & DIY.