Concrete Ramp Calculator

How to use this calculator

1. Measure the rise first: the vertical distance from the lower surface to the upper one. This is usually a step, a threshold or a curb height.
2. Measure the run: how far out from the upper surface the ramp will extend along the ground.
3. Enter the finished width of the ramp.
4. Pick the build. A solid wedge is all concrete. A slab over compacted fill uses gravel to make the shape and concrete only for the surface, which uses far less concrete on a long ramp.
5. Leave the waste allowance at 10% unless you are batching bags yourself.

If you choose the slab build, you also need base material. Size it with the gravel calculator.

Check the slope before you pour

A ramp that is too steep is worse than no ramp, and concrete is unforgiving once it sets. The calculator reports the slope as a ratio and a percentage so you can check it against the standard.

For an accessible ramp, the U.S. Access Board sets a maximum running slope of 1:12, which is about 8.3 percent, with a maximum cross slope of 1:48. That cross slope figure is a different problem from the running slope and it is the one that collides with drainage, because 1:48 is exactly the quarter inch per foot that ACI asks for to stop water ponding: the concrete slope calculator covers drainage fall and what pitching a surface costs in concrete. Flared sides on a curb ramp can be no steeper than 1:10, and a level landing at least 36 inches long is required at the top. Building one in the public right of way is a stricter job again, because PROWAG sets a 48 inch minimum width and allows no lip at all at the gutter: see our concrete curb ramp guide.

The practical consequence of 1:12 is worth doing in your head before you measure anything: every inch of rise needs a foot of run. A 7-inch step needs about 7 feet of ramp. A 30-inch porch needs 30 feet, which is usually when people start looking at a switchback with a landing instead of one straight run.

Vehicle ramps and utility ramps for a wheelbarrow or mower are a different matter and are often built much steeper. If the ramp is for a person using a wheelchair or walker, treat 1:12 as the ceiling rather than the target.

The formula

A solid ramp is a wedge, so its cross-section is a triangle. Half the rise times the run gives the cross-sectional area, and the width turns that into a volume:

Cubic yards = (Width ft × Run ft × Rise ft ÷ 2) ÷ 27

Worked example. A 4 ft wide ramp covering a 12 ft run to climb 12 inches: 4 × 12 × 1 ÷ 2 = 24 cubic feet, which is 0.89 cubic yards, or about 1 cubic yard with waste. That same ramp is a 1:12 slope, so it meets the accessible maximum.

The slab build is different. The concrete follows the slope rather than filling the wedge, so the length that matters is the sloped face, not the run:

Cubic yards = (Width ft × Slope length ft × Thickness ft) ÷ 27

For the same ramp at 5 inches thick, the slope length is 12.04 feet and the concrete drops to 20.1 cubic feet, about 0.74 cubic yards. The saving grows fast on a longer ramp, which is why most ramps over a few feet are built this way with compacted gravel underneath.

Practical notes

• Thickness. Four inches is the usual minimum for foot traffic, and 5 to 6 inches if a vehicle will ever drive on it. See concrete slab thickness.
• Reinforcement. A ramp is a slab on a slope, so the same rules apply. Our rebar and reinforcement guide covers mesh and bar sizing.
• Surface. Ramps need grip. A broom finish across the slope is standard, and a smooth trowel finish is the wrong choice on anything sloped.
• Base. Compact the fill properly. A ramp that settles at the bottom becomes a lip, and a lip on a ramp is a trip hazard.
• Landings. The flat area at the top is not part of the ramp volume. Calculate it separately with the concrete pad calculator.

Steps rather than a ramp, or both at the same entrance? The stairs calculator carries the IRC rise and run limits and the step volume, and how to build concrete steps covers the forms and the pour.