Staircase Concrete Basics: Volume of the Waist Slab + Steps

How Do You Calculate Concrete for a Staircase?

The concrete in a flight of stairs is the sloped waist slab plus the triangular volume of the steps, then a waste allowance:

Total = (waist slab volume) + (½ × rise × run × width × number of steps)

The waist slab is the inclined slab that carries the stairs; the steps are the triangular wedges sitting on top of it. Add a landing slab if there is one. A typical 12-step flight works out to a little over 1 cubic yard.

Quick start: The Staircase Concrete Calculator takes risers, treads, width, and waist thickness and returns the full volume with waste.

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Key Terms

• Riser — the vertical height of one step (typically 6–7.5 in).
• Tread / run — the horizontal depth you step on (typically 10–11 in).
• Waist — the thickness of the inclined structural slab beneath the steps (often 5–6 in).
• Going — the total horizontal length of the flight (steps × run).
• Landing — a flat slab at the top or mid-flight.

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Step 1 — Waist Slab Volume

The waist slab runs along the slope length of the stair, not the horizontal. Find the slope from the total rise and total going:

Slope length = √(total going² + total rise²)
Waist volume = slope length × width × waist thickness

Step 2 — Steps Volume

Each step is a right-triangle prism. Its volume is half the rise times the run times the width:

One step = ½ × rise × run × width
Steps total = one step × number of steps

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Worked Example

Flight: 12 steps, 7 in rise, 11 in run, 3.5 ft wide, 5 in waist.

Geometry (convert inches to feet):

• Total going: 12 × 11 in = 132 in = 11.0 ft
• Total rise: 12 × 7 in = 84 in = 7.0 ft
• Slope length: √(11² + 7²) = √170 = 13.04 ft

Waist slab:

• 13.04 × 3.5 × (5 ÷ 12 = 0.417) = 19.0 ft³

Steps:

• One step: ½ × (7 ÷ 12) × (11 ÷ 12) × 3.5 = ½ × 0.583 × 0.917 × 3.5 = 0.94 ft³
• 12 steps: 0.94 × 12 = 11.2 ft³

Total:

• 19.0 + 11.2 = 30.2 ft³ = 1.12 yd³ → order ~1.23 yd³ with 10% waste.

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Don't Forget the Landing & Supports

• Landing slab: add it as a flat slab — length × width × thickness ÷ 27. The method is the same as calculating concrete for a slab.
• Supporting footing or beam: a stair often bears on a footing or a hidden beam — those are separate pours. See the concrete footing calculations guide.
• Small pours: a one-flight stair is well under a yard, so bagged mix can make sense — check counts with how many bags of concrete for a slab.

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Frequently Asked Questions

How do you calculate the concrete volume of a staircase?

Add the waist slab to the steps. The waist slab is slope length × width × waist thickness; the steps total is ½ × rise × run × width × number of steps. Sum both and add a 5–10% waste allowance.

What is the waist of a staircase?

The waist is the inclined structural slab beneath the steps that carries the load down to the supports. It's usually 5–6 inches thick and is measured along the slope length, not the horizontal run.

How much concrete does a typical flight of stairs need?

A standard 12-step flight (7 in rise, 11 in run, 3.5 ft wide, 5 in waist) needs about 1.12 cubic yards — roughly 1.23 yards once you add waste. Add any landing slab separately.

What are standard riser and tread dimensions?

Risers are typically 6–7.5 inches and treads (runs) about 10–11 inches. Comfortable, code-compliant stairs keep risers consistent and pair a taller riser with a shorter tread.

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Summary

• Staircase concrete = waist slab + triangular steps + waste.
• Waist slab uses the slope length: √(going² + rise²) × width × thickness.
• Each step = ½ × rise × run × width.
• The 12-step example totals 1.12 yd³ (order ~1.23 yd³). Add landings separately.

Run your exact riser, tread, and width through the Staircase Concrete Calculator.

Related Guides

• How to Calculate Concrete for a Slab
• Concrete Footing Calculations
• How Many Bags of Concrete for a Slab

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