Concrete Stairs
Volume
Estimate the concrete volume for a flight of stairs: the triangular steps plus the inclined waist slab beneath them. Enter the geometry and get total volume with a waste allowance.
Who it's for: Architects, contractors, and quantity surveyors estimating concrete for a cast-in-place stair flight — you need the step count, rise, going, width, and waist slab thickness before pouring at construction.
How to use this calculator
The formula
Volume = Steps + Waist slab
Steps = n × ½ × rise × going × width
Waist slab = thickness × width × (n × √(rise² + going²))
n = number of steps | rise = vertical height per step | going = horizontal tread depth per step | thickness = waist slab depth
The term n × √(rise² + going²) is the true inclined length of the soffit — always longer than the horizontal plan projection. The calculator applies the user-entered waste percentage to the combined volume.
Worked example
When this estimate will be off
- Assumes a uniform waist slab thickness along the full inclined length. A slab that thickens at the bearing ends or at a landing junction needs a separate calculation for each zone.
- Does not include intermediate or top/bottom landings. Each landing should be calculated as a separate flat rectangular slab and added to the total.
- Assumes all steps are solid triangular fillets of concrete cast against the waist slab. Hollow forms, pre-cast step units, or stone-clad finishes will reduce or alter the pour volume.
- Rise and going must be identical for every step in the flight. If the top or bottom step is non-standard (common in renovation fit-out), exclude it and add a corrected volume manually.
Frequently asked questions
A common mistake: Assumes a uniform waist slab thickness along the full inclined length. A slab that thickens at the bearing ends or at a landing junction needs a separate calculation for each zone.
The waist slab is the inclined structural slab spanning between the landing levels. The triangular steps are cast on top of it as solid concrete fillets. Use the thickness specified by the project structural design; this volume calculator estimates material quantity and does not determine a structurally adequate thickness.
Use the dimensioned stair geometry from the current architectural or structural drawings. Rise is the vertical height of one step and going is its horizontal tread depth. Confirm that the entered dimensions use the same unit as the stair width and waist thickness, and verify code compliance separately.
No. The calculator covers only the inclined flight between two levels. Calculate each intermediate or end landing as a flat rectangular slab (length × width × thickness) and add those volumes to the stair flight total before placing a concrete order.
The 7% default is an editable estimating assumption, not a code requirement or guaranteed ordering factor. Set the percentage using the concrete supplier’s ordering rules and the contractor’s experience with the actual formwork, placement method, spillage, and overpour risk. Keep the arithmetic subtotal available for independent review.
Sources
- Calculation basis: elementary solid geometry — The flight is decomposed into n identical triangular step prisms plus one uniform inclined rectangular waist-slab prism. No controlling building-code standard governs this volume arithmetic.
- Implemented calculator method — The page calculates n × 0.5 × rise × going × width + thickness × width × n × √(rise² + going²), then applies the user-entered waste percentage. Landings are excluded.
This free Concrete Stairs Volume Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.