calcanvil

Concrete Ramp Calculator

24″volume = half the full prism
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Order 1.85-1.96 yd³

Wedge volume 48 ft³ (1.78 yd³ plan).

  • Wedge geometry: V = L × W × H ÷ 2. ADA slope limits (1:12) are a design constraint, not computed here.
  • NRMCA CIP-8 ordering allowance (4-10%) applied.

Why This One Is Different

Pouring a wheelchair approach, a garage threshold, or a loading-dock ramp and wondering why it needs less concrete than the flat slab next to it? This calculator computes that ramp's volume and applies the standard ordering allowance, but it doesn't check slope compliance for you. A concrete ramp tapers from zero to a set rise over its run, which makes it a wedge, not a rectangular slab, so it takes exactly half what a flat slab of the same footprint and rise would need (length times width times rise, divided by two). A 1:12 rise-to-run ratio is the common accessibility benchmark, and confirming it against your jurisdiction's adopted code is a separate step from ordering concrete.

Where the Numbers Come From

  • A ramp needs exactly half the concrete of a flat slab covering the same footprint and depth, because a wedge is half a prism: wedge volume = length × width × height ÷ 2, where height is the ramp's total rise. Source: worked example (closed-form geometry)
  • Order 4-10% more concrete than the wedge math says, the same as you would for a flat slab: NRMCA guidance calls for that allowance on any formed pour, tapered ramps included. Source: NRMCA, CIP 8: Discrepancies in Yield (2021 reprint)
  • A 1:12 rise-to-run ratio is a commonly cited accessibility slope benchmark, but it is a design/code constraint this calculator does not verify; confirm compliance against your jurisdiction's adopted accessibility code. Source: trade convention, labeled as such (not verified against a specific code section here)

More Questions

Does a ramp need a different concrete mix than a flat slab?

Not necessarily a different mix design, but exterior ramps exposed to freeze-thaw cycling often benefit from air-entrained concrete and a broom or textured finish for slip resistance; both worth discussing with your ready-mix supplier.

Related Calculators

Formulas, waste factors, and cost models on this page follow the sourced conventions on our methodology page. Estimates only; verify with your supplier and local code.