Table of Contents
Ramp Slope Basics
Ramp slope is the ratio of the vertical rise to the horizontal run. It is expressed as a ratio (1:12), a percentage (8.33%), or an angle (4.76 degrees). Proper slope calculation is critical for wheelchair accessibility, building code compliance, and safety.
The Americans with Disabilities Act (ADA) sets the maximum ramp slope at 1:12, meaning for every 1 inch of rise, you need 12 inches of run. Steeper slopes are harder to navigate in a wheelchair and may violate building codes.
Slope Formulas
ADA Requirements
- Maximum slope: 1:12 (8.33% grade) for new construction.
- Minimum width: 36 inches clear between handrails (48 inches recommended).
- Maximum rise per run: 30 inches before a landing is required.
- Landing size: Minimum 60 x 60 inches at the top, bottom, and where the ramp changes direction.
- Handrails: Required on both sides when the rise exceeds 6 inches, extending 12 inches beyond the top and bottom of the ramp.
- Edge protection: A minimum 2-inch curb or railing on both sides to prevent wheels from going over the edge.
- Surface: Must be firm, stable, and slip-resistant.
Slope Reference Table
| Slope Ratio | Grade (%) | Angle | Run per 1" Rise | Use Case |
|---|---|---|---|---|
| 1:20 | 5.0% | 2.9° | 20" | Gentle / elderly-friendly |
| 1:16 | 6.25% | 3.6° | 16" | ADA preferred |
| 1:12 | 8.33% | 4.8° | 12" | ADA maximum |
| 1:10 | 10.0% | 5.7° | 10" | Non-ADA, curb ramps |
| 1:8 | 12.5% | 7.1° | 8" | Steep, assisted use only |
| 1:6 | 16.7% | 9.5° | 6" | Vehicle ramps only |
Frequently Asked Questions
How long does a ramp need to be for 3 steps?
Three standard steps have a total rise of about 21-24 inches. At the ADA maximum slope of 1:12, you need 252-288 inches (21-24 feet) of ramp run. At the preferred 1:16 slope, you need 336-384 inches (28-32 feet), which may require a switchback design.
What is the maximum slope for a wheelchair ramp?
The ADA maximum slope is 1:12 (8.33%). For existing buildings where space is limited, a slope of 1:10 may be permitted for a maximum rise of 6 inches, and 1:8 for a maximum rise of 3 inches. However, 1:16 or gentler is strongly recommended for independent wheelchair use.
Do I need a landing on my ramp?
Yes, ADA requires a level landing at the top and bottom of every ramp. Additionally, a landing is required every 30 inches of rise. Each landing must be at least 60 inches long and at least as wide as the ramp. Landings at turns must be 60 x 60 inches minimum.