What this calculator does
Staircases take surprisingly little concrete for how much formwork they need. This calculator splits the pour into its three parts — the sloping waist slab, the triangular steps and the landing — so you can order the right volume and check the shuttering quantity.
How to use it
- Enter the number of risers, the riser height and the tread depth; these must be a consistent pitch.
- Enter the waist thickness, usually 100–150 mm for a reinforced concrete flight.
- Enter the flight width and, if there is one, the landing length.
- Add 5–10 % waste before ordering, and remember the stair flights usually need a separate pour.
Governing formula
L = √((n·g)² + (n·r)²) ; V = L·t·w + n·(½·r·g·w) Where:
-
n= Number of risers [–] -
r= Riser height [m] -
g= Tread depth [m] -
t= Waist thickness [m] -
w= Flight width [m]
Worked example — 16 risers at 175 mm with a 1.2 m wide flight
The figures below were produced by running this page's own engine with the example inputs (Number of risers, Riser height (mm), Tread depth (mm), Waist thickness (mm), Flight width (m), Landing length (m)). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Total concrete volume | 1.4 m³ |
|---|---|
| Waist slab volume | 0.76 m³ |
| Steps volume | 0.47 m³ |
| Landing volume | 0.17 m³ |
| Sloping slab length | 5.28 m |
| Flight rise | 2.8 m |
| Flight going | 4.48 m |
| Assessment | Flight rise 2.80 m over 4.48 m going; slab ≈ 5.3 m long → ≈ 1.40 m³ of concrete (waist 0.76 + steps 0.47 + landing 0.17). |
- The flight rises 2.8 m over a going of 4.48 m, giving a sloping slab length of 5.28 m.
- The waist slab is 5.28 × 0.12 × 1.2 = 0.76 m³, and the steps add about 0.47 m³.
- With the landing the flight needs roughly 1.4 m³ of concrete.
Assumptions & limitations
Engineering calculation. Waist slab, triangular steps and landing volumes from geometry. It assumes a constant waist thickness measured perpendicular to the soffit and excludes beams, upstands and landings at a different thickness.
- Geometric volume only — no reinforcement, formwork area or structural design.
- Assumes one landing at the waist thickness; landings are often thicker.
- Does not deduct for openings or ducts, which rarely matter for a staircase.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- BS 8500-2 — construction of reinforced concrete stairs.
- EN 1992-1-1 — design of concrete staircases.