Volume and bag count for slabs, footings, columns, walls and stairs
Bag yields: 0.60, 0.45 and 0.30 ft³ for 80, 60 and 40 lb premix. Waste included.
| Shape | Volume |
|---|---|
| Slab or footing | L × W × T |
| Round column | π/4 × D² × H |
| Square column | B × D × H |
| Wall | L × H × T |
| Stairs (n steps) | W × run × rise × n(n + 1)/2 |
1 yd³ = 27 ft³ = 0.7646 m³. Convert inches to feet (÷ 12) before multiplying, or use the unit converter.
For a single shape with its own page, see the slab calculator and the footing calculator. To estimate the steel, use the rebar calculator.
Multiply length × width × thickness in feet to get cubic feet, then divide by 27. A 10 ft × 10 ft slab 4 in thick is 10 × 10 × 0.333 = 33.3 ft³, or 1.23 yd³.
About 45. An 80 lb bag of premix yields roughly 0.60 ft³, and a cubic yard is 27 ft³, so 27 / 0.60 = 45 bags. With 60 lb bags (0.45 ft³) it is 60 bags; with 40 lb bags (0.30 ft³) it is 90.
Add 5 to 10 percent for uneven subgrade, form deflection and spillage. Use the high end for footings dug in soil, where trench walls are rarely straight.
Each step is treated as a solid block on grade. Step i has height i × rise, so the total is width × run × rise × n(n + 1) / 2 for n steps.