When to use: Convert between rise/run, percent slope, slope angle, and ratio for walkways, ramps, and graded surfaces. % slope = rise / run × 100. The ADA check adapts to the selected mode: running slope of an accessible route must be ≤ 5% (1:20), with ramps permitted up to 8.33% (1:12) when handrails and landings are provided; cross slope must not exceed 2% (1:48).
This calculator converts between rise and run, percent slope, angle in degrees, and slope ratio for walkways, ramps, driveways, and graded surfaces — and instantly checks compliance with ADA accessibility standards for both running slope and cross slope, making it essential for site design and permit documentation.
Percent slope = (rise / run) × 100, where rise is the vertical elevation change and run is the horizontal distance. This is the most common form used in civil engineering, grading plans, and drainage design. Slope angle in degrees = arctan(rise / run). Slope ratio is expressed as rise:run (e.g., 1:12 means 1 ft vertical for every 12 ft horizontal).
For drainage design, minimum slopes ensure positive drainage: 1% minimum on paved surfaces, 2% minimum on grassed areas, and 0.5% minimum on concrete gutters. Maximum slope on grass before erosion control measures are required is typically 3:1 (33%) with riprap or 2:1 (50%) with geotextile matting. For highway cross slopes, 2% is standard; superelevated curves may have up to 8% (or 10% in some states).
ADA Standards for Accessible Design (2010 ADA Standards, based on ANSI A117.1) specify: accessible routes ≤ 5% running slope (1:20); ramps ≤ 8.33% (1:12) with handrails when slope exceeds 5%; cross slopes ≤ 2% (1:48) on all accessible routes including sidewalks, parking, and ramps. IBC Section 1012 provides the same ramp slope limits. AASHTO highway design standards permit cross slopes up to 4% on tangent sections and 8–10% on superelevated curves.
For parking lots, minimum drainage slope is typically 1–2% per ITE and local drainage ordinances. Maximum driveway slope is governed by local codes, typically 10–15% for residential and 8–12% for commercial access, with a maximum of 20% in some jurisdictions for short distances.
ADA running slope and cross slope requirements apply to the entire accessible route from public right-of-way to building entrance, including sidewalks, parking aisles, curb ramps, and plazas. A common design error is failing to account for cross slopes exceeding 2% at curb ramp wings or where drainage cross slopes intersect the accessible route.
For grading plans, slopes steeper than 3:1 (33%) require erosion control measures; slopes steeper than 2:1 (50%) require retaining walls or rock armoring. OSHA regulations require stable slopes or shoring for excavations deeper than 5 ft. On final grading plans the minimum grade away from buildings is typically 5% for the first 10 ft per IBC and most local grading codes.
Enter the rise (vertical elevation change in feet) and run (horizontal distance in feet). Select Running Slope for walkways, ramps, and graded routes along the direction of travel, or Cross Slope for the slope perpendicular to travel. The calculator displays percent slope, angle, ratio, and an ADA compliance status indicator. For ramp design, ensure running slope stays within 8.33% and add the required 5 ft × 5 ft level landing at both ends.
The 2010 ADA Standards limit ramp running slope to 1:12 maximum (8.33%). Ramps must have handrails on both sides when the rise exceeds 6 inches, and level landings at least 60 in × 60 in at the top and bottom. The minimum clear width is 36 inches. Edge protection (curb, barrier, or extended surface) is required where the ramp is not bounded by a wall.
Paved parking lots require a minimum 1% slope for positive drainage, with 2% preferred to prevent ponding from low spots due to construction tolerances. Maximum slope in accessible parking stalls and access aisles is 2% in any direction per ADA requirements. Where parking is on a sloped site, accessible spaces must be located on the flattest available area, typically near the building entrance.
Local codes vary, but typical maximums are 12–15% for residential driveways and 10% for commercial driveways. The connection to the public street typically must flatten to 5% or less for a minimum 20 ft transition to ensure adequate sight distance and vehicle approach clearance. AASHTO provides design guidance for driveway grades based on vehicle approach speeds.
A 1:3 slope (1 ft rise per 3 ft run) equals 33.3% grade or 18.4 degrees. This is at the upper limit of what typical lawn mowers can maintain and is the commonly cited maximum for grass slopes without erosion control measures. Steeper slopes (1:2 = 50%, 1:1 = 100%) require structural erosion control such as erosion control blankets, riprap, or retaining walls.
The minimum slope for a vegetated swale is typically 0.5–1.0% to prevent standing water and sediment accumulation. Concrete-lined channels can function at 0.1–0.2% minimum. The design should also check that velocity at the minimum slope exceeds 1.5–2.0 ft/s to remain self-cleaning, while not exceeding the maximum non-erosive velocity for the lining material.