How Much Concrete Do You Need for Stairs?
Part of Concrete & Masonry
Quick answer
For a solid flight of n steps, volume = width × run × rise × [1 + 2 + … + n] (all in feet). Each step further back rests on another layer of concrete, so the steps add up like 1+2+3+… A 4-step flight at 7 in rise, 11 in run and 3 ft wide is about 16 ft³ — roughly 0.6 cubic yards, or 27 × 80 lb bags.
Poured concrete stairs are solid, so the concrete isn't just the steps you see — it's the whole stepped mass underneath them. The trick is that each step toward the back sits on top of everything in front of it.
The formula
Cubic feet = width ft × run ft × rise ft × [1 + 2 + … + n]
The bracket is the sum 1 + 2 + … + n for n steps, which equals n × (n + 1) ÷ 2. For 4 steps that's 4 × 5 ÷ 2 = 10. Convert the rise and run from inches to feet (divide by 12) before multiplying.
Concrete by step count
| Steps | Sum 1+…+n | Volume (7 in rise, 11 in run, 3 ft wide) | 80 lb bags |
|---|---|---|---|
| 2 | 3 | 4.8 ft³ (0.18 yd³) | 9 |
| 3 | 6 | 9.6 ft³ (0.36 yd³) | 17 |
| 4 | 10 | 16.0 ft³ (0.59 yd³) | 27 |
| 5 | 15 | 24.1 ft³ (0.89 yd³) | 41 |
| 6 | 21 | 33.7 ft³ (1.25 yd³) | ready-mix |
Add a top landing as an extra solid block (width × landing depth × full height). Past about a cubic yard — roughly 5–6 steps at this size — ordering ready-mix is cheaper than mixing bags.
FAQs
How many bags of concrete per step?
It grows as you add steps because each step sits on the ones below. For a 3 ft-wide flight at 7 in rise and 11 in run, the first step is about 1.6 ft³ (3 bags), but a 4-step flight totals about 16 ft³ (27 bags), not 4 × the first step.