How to calculate concrete for steps
Solid concrete steps are a staircase-shaped block. Seen from the side, each step is a column one riser taller than the one before, so the side profile adds up to rise × tread × (n − 1) × n ÷ 2, where n is the number of step-ups. A landing on top adds n × rise × landing depth. Multiply the profile (in square inches) by the width and divide by 144 for cubic feet:
Volume = W × [R × D × (n − 1)·n ÷ 2 + n × R × P] ÷ 144 — W in feet, rise R, tread D and landing P in inches.
Worked example — 3 steps, 7 in rise, 11 in treads, 4 ft wide, 36 in landing: 7 × 11 × 6 ÷ 2 = 231 sq in for the steps, 3 × 7 × 36 = 756 sq in for the landing. 987 sq in ÷ 144 × 4 ft = 27.4 cu ft (1.02 yd³). With 10% extra: 51 × 80-lb bags. The same steps running up to an existing porch need only 6.4 cu ft — 12 bags. The landing is most of the concrete.
Rise, tread and landing rules
- Risers: 7.75 in maximum (IRC R311.7.5.1), measured between tread edges. Divide the total height by 7¾ and round up for the number of steps; the calculator's height mode does it for you.
- Treads: 10 in minimum (R311.7.5.2). Below 11 in, the code wants a ¾–1¼ in nosing, which is awkward in concrete — so most concrete steps use 11–12 in treads.
- Consistency: the tallest riser and the deepest tread may differ from the smallest by no more than ⅜ in within a flight. Uneven steps trip people.
- Landings: an exterior door needs a landing at least 36 in deep and as wide as the door (R311.3), sloped no more than 2%. It may sit up to 7¾ in below the threshold if the door does not swing over it.
- Handrails and guards: 4 or more risers need a handrail 34–38 in high (R311.7.8). A landing more than 30 in above grade needs a guard on its open sides (R312.1).
Concrete for common step sizes
| Steps (7 × 11 in) | Cu ft | 80-lb bags (+10%) |
|---|---|---|
| 2 steps, 3 ft wide + 36 in landing | 12.1 | 23 |
| 2 steps, 4 ft wide + 36 in landing | 16.1 | 30 |
| 3 steps, 3 ft wide + 36 in landing | 20.6 | 38 |
| 3 steps, 4 ft wide + 36 in landing | 27.4 | 51 |
| 3 steps, 5 ft wide + 36 in landing | 34.3 | 63 |
| 3 steps, 4 ft wide to a porch | 6.4 | 12 |
| 4 steps, 4 ft wide + 36 in landing | 40.8 | 75 |
| 4 steps, 5 ft wide to a porch | 16 | 30 |
| 5 steps, 4 ft wide to a porch | 21.4 | 40 |
| 5 steps, 5 ft wide + 36 in landing | 70.5 | 130 |
Mix, forms and base
Steps sit out in the weather and take de-icer. IRC Table R402.2 asks for 3,000 psi in moderate climates and 3,500 psi where weathering is severe, air-entrained to 5–7%. Regular bagged mix has no added air; Quikrete's Crack-Resistant mix lists 4–8%, or order air-entrained ready-mix.
Form the sides from plywood cut to the stair profile and the front of each step from a board ripped to the riser height, braced so the wet concrete cannot push it out. Bevel the bottom edge of each riser board so you can finish the tread right up to it. Set the steps on compacted gravel — the calculator assumes 4 in, the IRC base course under slabs — and where the ground freezes, ask your building department whether steps attached to the house need their own footings.
Common mistakes
- Counting treads instead of step-ups — the landing or porch is the last step, so count the risers.
- Forgetting the landing in the estimate: on a 3-step stoop it is about three-quarters of the concrete.
- Making the top riser shorter or taller than the rest to “catch up” — keep them within ⅜ in.
- Pouring in several batches hours apart; plan enough crew or order ready-mix so the whole stair goes in at once.
Pouring a walkway to the steps? Use the slab calculator. Need footings under the steps or a porch? Try the footing calculator.