Concrete Stairs Calculator
Estimate concrete for a solid poured stair flight from width, rise, run, and step count.
Content updated September 14, 2026
Models a solid, monolithically poured flight as stacked rectangular slabs — one step shorter with each step up. It does not model a hollow-formed stair over a sloped subgrade, metal pan stairs, landings, stringers, or a separate footing. Riser and tread sizing, reinforcement, and safe construction are structural and code decisions — verify with a qualified professional.
Estimate the concrete volume for a solid, monolithically poured stair flight from its width, the rise and run of each step, and the number of steps.
A stair flight is not a rectangular prism or a cylinder — modeled as solid stacked slabs, each step's slab is one step shorter than the one below it, so the total profile area follows a triangular-number summation rather than a single length-times-width or radius-squared formula.
The Concrete Stairs formula
Net volume = width × rise × run × steps × (steps + 1) ÷ 2 · order volume = net volume × (1 + allowance% ÷ 100) · bags = ceiling(order ft³ ÷ yield ft³/bag)Width, rise, and run are converted to a common unit before multiplication · steps × (steps + 1) ÷ 2 is the nth triangular number for the step count · 1 yd³ = 27 ft³ exactly.
Worked example
A 36 in wide flight of 4 steps, each with a 7 in rise and 11 in run, has a net volume of about 16.042 ft³. With a 10% allowance the order volume is about 17.646 ft³ (0.654 yd³); at 0.6 ft³ per bag that is 29.410 bags, rounding up to 30.
Assumptions, rounding, and limitations
Assumptions
- The flight is a solid, monolithically poured structure modeled as n stacked rectangular slabs, each one step shorter than the slab below it.
- Width, rise, and run are constant across every step.
- The entered contingency percentage is applied directly to net volume.
Rounding: Volume math retains floating-point precision. Displayed volumes show up to three decimal places; the purchase-oriented bag result always rounds the exact quotient upward to a whole bag.
Limitations
- Does not model landings, stringers, a separate footing, hollow-formed or metal-pan stairs, reinforcement, or supplier batch increments.
- Does not determine riser height, tread depth, or width — those are structural and local-code decisions.
- The result is a planning estimate and should be checked against approved drawings and field measurements.
Sources
- CIP 31 — Ordering Ready Mixed Concrete — National Ready Mixed Concrete Association
- NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
Why stairs use a different formula
Picture the flight built from the bottom up: the bottom slab runs the full length under every step above it, the next slab is one step shorter, and so on to the top step, which is just one run long. Adding those lengths together (n + (n-1) + ... + 1) gives n(n+1)/2, the nth triangular number, so total volume equals width × rise × run × n(n+1)/2.
NRMCA's 4%–10% contingency guidance for ready-mix orders applies here too; the default allowance is 10% but stays editable for a project-specific decision.
What this does and does not model
This models a solid poured flight only — no landing, no separate footing, and no hollow-formed stair over a sloped subgrade or metal pan, all of which use meaningfully less concrete than a fully solid pour.
Riser height, tread depth, and stair width are governed by local building code and are not checked or assumed here; enter the dimensions from your own approved plan.
Frequently asked questions
▶How do I calculate concrete for stairs?
Multiply width × rise per step × run per step × the nth triangular number for your step count (n(n+1)÷2), then apply your chosen contingency allowance.
▶Why isn't this just length × width × height like a slab?
A stair flight's cross-section is a set of stacked steps, not a single rectangle, so its volume needs a summation across steps rather than one multiplication.
▶Does this include the stair footing or a landing?
No. It models only the stepped flight itself. A footing beneath the stairs or a landing slab needs to be calculated separately, for example with the footing or slab calculator.
▶Does this tell me what rise and run I'm allowed to use?
No. Riser height and tread depth are set by local building code, and this calculator does not check or assume compliance — use the dimensions from your approved plan.
▶Will hollow-formed or metal-pan stairs need this much concrete?
No. This models a fully solid poured flight. A stair built over a sloped subgrade, void form, or metal pan uses less concrete than the solid-block model here, sometimes substantially less.
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Open calculator →Disclaimer: Concrete Stairs Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.