Concrete Stairs Calculator
Concrete volume for a poured stair flight.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Step wedges = ½ × riser × tread × steps × width
Throat slab = √(Total rise² + Total run²) × throat thickness × width
Volume = step wedges + throat slab
Run the calculation to see each step with your own numbers.
A 7-step stair, 4 ft total rise, 5 ft total run, 3 ft wide, 6 in throat, 10% waste.
Riser = 48 in ÷ 7 = 6.86 in; tread = 60 in ÷ 7 = 8.57 in
Wedges ≈ ½ × 0.571 × 0.714 × 7 × 3 ≈ 4.28 ft³
Throat ≈ √(4² + 5²) × 0.5 × 3 ≈ 9.60 ft³ → total ≈ 13.9 ft³ ≈ 0.52 yd³ → order 0.57 yd³
- A straight flight with uniform risers and treads on a solid sloped slab (not open-riser stringers).
- No landing at top or bottom beyond the throat slab meeting grade — add a landing separately.
- Nosing overhangs are ignored (they add a negligible amount).
- Side forms/cheek walls are not included.
- Do I include a bottom landing?
- No — this covers the flight and its structural slab. Add the landing as a separate rectangular pour with the Concrete Calculator.
- What throat thickness should I use?
- The throat is the solid slab under the steps, measured square to the slope. 5–6 in is common for a short residential flight on grade; a longer span or a cantilevered stair needs an engineered thickness — enter what your drawings specify.
- The riser height came out over 7¾ inches — what now?
- Add a step and recalculate. More steps gives a shorter riser but a longer run, so check the run still fits your opening.
Geometry
Standard geometry — triangular prisms + a sloped slab. Unit conversions per NIST SP 811.
Riser range
IRC R311.7.5 (maximum riser 7¾ in). Shown for reference only — BuildFactor does not enforce code.
About the Concrete Stairs Calculator
The Concrete Stairs Calculator estimates the concrete for a poured flight — the triangular step wedges plus the sloped structural slab (the throat) beneath them — from the total rise, total run, number of steps, width and throat thickness. It also returns the resulting riser height so you can check it against a comfortable range and adjust the step count. Landings, cheek walls and any footing at the base of the flight are poured separately.
What you enter
- Total rise — Finished floor to finished floor (or grade to landing).
- Total run — Horizontal distance the stair covers.
- Number of steps (risers)
- Stair width
- Throat slab thickness — The structural slab beneath the steps, measured perpendicular to the slope.
- Waste allowance — Default 10%. Adjust to your own allowance — the exact figure is always shown too.
What you get back
- Concrete volume — shown as the exact figure and, separately, a recommended figure with your waste allowance added.
- Riser height — Aim for 4–7¾ in per the IRC; adjust the step count if this is outside that range.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Concrete Calculator — How much concrete a rectangular slab or footing needs, in cubic yards or cubic metres.
- Stair Calculator — Stair rise, run, stringer length and step count for a total height.
- Concrete Footing Calculator — Concrete volume for strip and pad footings.
Part of the Concrete calculators.