Concrete Stairs Calculator
Calculate concrete volume in cubic yards, cubic feet, and 80-lb bags for poured stairs from step count, riser height, tread depth, and width.
How this calculator works
Poured stairs form a stepped wedge of concrete. Because each step rests on everything below it, the total volume is the sum of every step’s block — which works out to riser × tread × n(n+1)/2 across the stair width.
Formula: Cubic inches = width × riser × tread × [n(n+1) ÷ 2], where n is the step count. Divide by 46,656 for cubic yards; each 80-lb bag yields 0.6 cubic feet.
Worked example
A 4-step stair, 7-inch risers, 11-inch treads, 4 feet wide:
- Step sum: 4 × 5 ÷ 2 = 10 step-units
- Cubic inches: 48 × 7 × 11 × 10 = 36,960 in³
- Cubic yards: 36,960 ÷ 46,656 ≈ 0.79 yd³
- Cubic feet: ≈ 21.39 ft³
- 80-lb bags: ⌈(0.79 × 27) ÷ 0.6⌉ = 36 bags
Reference
| Steps (7 in × 11 in, 4 ft wide) | Cubic yards |
|---|---|
| 3 steps | 0.48 yd³ |
| 4 steps | 0.79 yd³ |
| 5 steps | 1.19 yd³ |
How to measure
Decide your step count, riser height, and tread depth (the Stair Calculator gives comfortable values), then measure the stair width. Add rebar and a footing, and order a little extra concrete so you never run short during the pour.
Poured stairs are structural. Confirm reinforcement and footing size with local code.
Frequently asked questions
How is concrete stair volume calculated?
A staircase is a stepped solid: each step sits on all the concrete below it, so the bottom step is the tallest block and the top the shortest. Summed together, the cross-section equals riser × tread × n(n+1)/2, multiplied by the stair width. This calculator does that sum for you.
Should I order ready-mix or bags?
Below about a cubic yard (roughly 45 eighty-pound bags), bags are practical. A typical short flight lands near that line, so the calculator shows both cubic yards and bag count — compare against your effort and budget. A cold joint from running short mid-pour weakens the stairs, so order a little extra.
Do concrete stairs need rebar?
Yes — poured stairs need reinforcement to resist cracking and to tie into the footing or slab below. Use the Rebar Calculator to size the steel, and set the bars before the pour.
What riser and tread should I use?
The same comfort rules as any stairs: risers around 7 inches, treads 11 inches or more, with 2×riser + tread near 24–25 inches. Use the Stair Calculator to find comfortable step dimensions, then bring the step count here for the concrete volume.
Does this include the landing or footing?
No — this is the stepped stair mass only. Add the volume of any top landing slab and the footing beneath the bottom step separately using the Concrete Calculator.
Estimates only. Verify quantities with your supplier before purchasing.