Concrete Stairs Calculator
The concrete volume for a flight of stairs — the steps plus the waist slab beneath — with the step geometry checked against the usual rule.
Concrete for a stair flight.
How the concrete stairs calculator works
A concrete stair is two volumes: the triangular prisms of the steps themselves, and the sloping waist slab underneath them.
The steps come to (rise × going ÷ 2) × width per step. The waist is the slope length × its thickness × width. Both are needed — leaving out the waist under-orders by a third or more.
Formula: V = n(rise × going / 2)w + (slope length × waist × w)
Worked examples
| Inputs | Total concrete | Note |
|---|---|---|
| 12 steps, 175 rise, 280 going | 0.977 | 0.94 m³ with waste |
| A steeper flight | 0.935 | 43° — steep but legal in many codes |
| A wider stair | 1.466 | half as much again |
FAQFrequently asked questions
Do I need to include the waist slab?
Yes, always. It is the structural part, and on a typical flight it is nearly as much concrete as the steps themselves.
What is the 2R + G rule?
Twice the rise plus the going should land between about 550 and 700 mm. It is the oldest and most reliable test of whether a stair feels right underfoot.
How thick should the waist be?
125 to 175 mm for a domestic flight, but it is a structural question — span, load and reinforcement decide it, and an engineer should.
What rise and going should I use?
Around 175 mm rise and 280 mm going is comfortable. Codes set limits — check the one that applies where you are building.
Can I pour stairs in one go?
Yes, and you should. Use a riser-board form and start from the bottom step; the mix wants to be stiff or it will slump out of the risers.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Cement Concrete & Aggregates Australia — concrete basics and yields — bag yields, density 2,400 kg/m³
- Australian Building Codes Board — the National Construction Code
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.