Concrete Ramp Volume and ADA Slope Calculator

ADA ramp requirements ensure wheelchair accessibility for buildings and public spaces. The Americans with Disabilities Act (ADA) sets specific standards for slope, width, and landings.

ADA slope requirement: Maximum slope = 1:12 (for every 1 inch of rise, 12 inches of run)

This means: Ramp Length = Rise × 12

For a 30-inch rise: 30 × 12 = 360 inches = 30 feet of ramp length.

ADA ramp standards:

If the total rise exceeds 30 inches, you need multiple ramp runs with intermediate landings.

Number of runs formula: Runs = Ceiling(Total Rise / 30 inches)

Concrete volume for ramp: The ramp forms a triangular prism: Volume = (Rise × Run × Width) / 2

For imperial: convert to cubic yards by dividing cubic inches by 46,656. Landings are costed on top as 4-inch slabs.

That triangular prism is a solid wedge of concrete, and it is the honest figure only if you are actually pouring one. Past about a foot of rise almost nobody does. The usual build is compacted fill or a stem wall with a 4 to 6 inch slab over it, which uses a fraction of the concrete and a good deal more formwork and rebar. A 30-inch rise at 1:12 and 4 feet wide is 5.6 cubic yards of wedge, against about 1.9 for a 5-inch slab riding on fill. Its two landings add another 0.5 either way, so the figure below reads 6.05.
Use the figure below when you are pouring solid, and treat it as an upper bound otherwise. Either way, order about 10% over: concrete is cheap and a second truck is not.

Slope percentage conversion:

• 1:12 = 8.33%
• 1:16 = 6.25% (recommended for comfort)
• 1:20 = 5.00% (ideal for self-propelled wheelchair users)

Practical tips:

• A gentler slope (1:16 or 1:20) is much easier for wheelchair users to navigate independently.
• Add non-slip surface treatment to concrete ramps.
• Ensure drainage so water does not pool on the ramp surface.
• In cold climates, consider heated ramp surfaces to prevent ice formation.
• Top and bottom landings must be level (max 2% slope for drainage).

Not pouring concrete? The ADA ramp calculator does the same slope and landing arithmetic without the material take-off, and it goes past the ADA range: pallet jack at 7%, forklift at 10%, a vehicle approach at 15%, plus 1:20, which the ADA treats as a walking surface rather than a ramp and so exempts from handrails and intermediate landings. It also gives the sloping surface length, which is what you order decking and stringers by.
Both run the same numbers. A 24-inch rise at 1:12 is a 24-foot run and 34 feet of total length with landings on either page.