Concrete Stairs Calculator
Enter the number of risers, your rise and tread run, the width and the throat, and this calculator returns the concrete volume for the stair — cubic yards to order, bag count and weight. The rise and run are yours: this tool converts the geometry you enter, it never tells you what the geometry should be.
Concrete to order
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Results are estimates for planning purposes. Verify with your supplier, engineer, or a qualified professional before ordering material or performing work.
The two shapes, and why the volume differs
A stair is a prism: work out the cross-section once, multiply by the width. What changes between jobs is the underside.
- Suspended slab. The underside is a plane. The section is the big wedge (total rise × total run ÷ 2), plus one half-step triangle per tread — the sawtooth that sits above that plane — plus the throat, which is a constant thickness measured perpendicular to the slope, so it multiplies the slope length √(H² + L²).
- On grade. The excavation or the fill is cut square under each step, so every tread strip is a block standing on the base: 1, 2, 3 … times the rise. The section is rise × run × treads × (treads + 1) ÷ 2.
Both are in the selector. If your stair sits on compacted fill that follows the slope, the suspended figure with a small throat is the closer model; if the crew is stepping the subgrade, use the on-grade figure. When you are unsure, price the larger of the two — running short mid-pour on a stair is a cold joint across the nosing.
Worked examples, 4 ft wide, 7 in rise, 11 in tread
| Risers | Treads | Total rise | Suspended, 5 in throat | On grade |
|---|---|---|---|---|
| 3 | 2 | 21 in | 0.47 yd³ | 0.24 yd³ |
| 4 | 3 | 28 in | 0.82 yd³ | 0.48 yd³ |
| 5 | 4 | 35 in | 1.24 yd³ | 0.79 yd³ |
| 6 | 5 | 42 in | 1.74 yd³ | 1.19 yd³ |
| 7 | 6 | 49 in | 2.32 yd³ | 1.66 yd³ |
| 8 | 7 | 56 in | 2.99 yd³ | 2.22 yd³ |
Net volume from the geometry, before any waste allowance, with the top riser landing on an existing slab. These are examples of the arithmetic, not a recommended stair: the rise and run in your job come from your drawings and the code your jurisdiction adopted.
Before you pour
- Order more than the paper volume. NRMCA TIP 8, citing ASTM C94, lists why the truck comes up short: waste, spillage, loss of air content, settlement, form deflection, over-excavation. A stair has forms on three sides and a lot of edge — the waste field above is that allowance.
- Rise, run and reinforcement are not ours to set. Uniformity of rise, tread depth, nosing, handrails, bar size, cover and the footing under the stair all come from the adopted building code and your drawings. This page does arithmetic on the numbers you enter.
- Landings are a separate pour to calculate. A landing is a slab: length × width × thickness. The concrete slab calculator handles it, and the volumes simply add.
- Weight. At 145 lb/ft³ (NRMCA CIP 36 gives 140 to 150 for normalweight concrete), a 5-riser stair at 4 ft wide is close to 4,900 lb. Forms, ties and the ground under them carry that before it cures.
- Steel is counted separately. For bars and total weight in the stair and its footing, use the rebar calculator with the spacing on your drawings.
How it's calculated
- Geometry
total rise H (in) = risers × rise ; total run L (in) = treads × run ; treads = risers − 1 or risers- Cross-section, suspended stair
A (in²) = H × L / 2 + treads × rise × run / 2 + throat × √(H² + L²)The stepped mass above the sloped underside is the wedge H × L / 2 plus one half-step triangle per tread; the throat is the slab thickness measured perpendicular to the soffit, so it multiplies the slope length.- Cross-section, stair on grade
A (in²) = rise × run × treads × (treads + 1) / 2Each tread strip sits on a square-cut base, so its height above the bottom of the first riser is 1, 2, 3 … times the rise. This is the form volume when the excavation follows the steps rather than a slope.- Volume
V (ft³) = A (in²) / 144 × width (ft) ; yd³ = ft³ / 27- Volume to order
V order = V × (1 + waste % / 100)- Weight
weight (lb) = V (ft³) × 145 lb/ft³Normalweight concrete runs 140 to 150 lb/ft³ (NRMCA CIP 36). This calculator uses 145.- Bags
bags = ceiling( V order / yield per bag )QUIKRETE Concrete Mix No. 1101 yields 0.60 ft³ per 80 lb bag, 0.45 per 60 lb and 0.30 per 40 lb. Above roughly a cubic yard, bagged mix stops being reasonable: a yard is 45 bags of 80 lb, or 3,600 lb to carry and mix.
Frequently asked questions
For a 4 ft wide suspended stair with five 7 in risers, 11 in treads and a 5 in throat, the geometry gives about 33.5 ft³, or 1.24 cubic yards before waste. Change any one of those numbers and the answer moves — a foot of extra width adds a quarter of a yard.
Work out the cross-section of the stair in square inches, then multiply by the width. For a suspended stair the section is the wedge (total rise × total run ÷ 2) plus half a step per tread plus the throat times the slope length; on grade, it is the sum of the step blocks, rise × run × treads × (treads + 1) ÷ 2. Divide by 144 to get square feet.
One fewer tread than risers when the top riser lands on an existing slab, deck or landing — the landing is the last walking surface. If the stair pours its own top tread, the counts match. Both cases are in the selector, because they change the total run and the volume.
Past about a cubic yard, ready-mix. A cubic yard is 45 bags of 80 lb mix — 3,600 lb to buy, carry, open and mix, in a pour where the concrete has to stay stiff enough to hold a step edge. Short-load charges from a ready-mix plant usually beat that.
The slab thickness under the steps, measured perpendicular to the sloped underside. It carries the stair, so it comes from your drawings or your engineer — it is an input here, never an output.
No. Rise and run limits, uniformity tolerances, nosing and handrail requirements come from the building code your jurisdiction adopted and from your drawings. This tool converts the geometry you enter into a concrete volume; it does not verify that the geometry is legal where you are.
About 145 lb per cubic foot, so roughly 3,915 lb per cubic yard — the 33.5 ft³ example above is about 4,860 lb of concrete. That weight is why a stair needs a designed footing or a designed slab under it, not just compacted fill.
Sources & references
- NRMCA CIP 36 — Structural Lightweight Concrete: normalweight concrete density range, 140 to 150 lb/ft³
- NRMCA TIP 8 — Concrete Yield: why the concrete placed exceeds the volume calculated from the dimensions (waste, spillage, over-excavation, form deflection, settlement), per ASTM C94
- QUIKRETE Concrete Mix No. 1101 — product data sheet: yield per bag and mixing water
Content checked against these sources — last reviewed August 29, 2026.