Square Feet to Cubic Feet Calculator
Area can't become volume without a depth. Enter your square footage and a depth in inches to get cubic feet, cubic yards, and tons for mulch, concrete, gravel, soil, or sand.
Last updated:Material: Mulch 3" — tons use loose bulk density (mulch ~25, concrete ~150, gravel ~100, topsoil ~95 lb/ft³).
How the Conversion Works
Cubic feet = square feet × (depth in inches ÷ 12). Cubic yards = cubic feet ÷ 27. Tons = cubic feet × material density ÷ 2,000.
Area measures a surface; volume measures what fills it. That's why "sq ft to cft" always needs a third dimension — see our square feet vs cubic feet guide for when each unit applies.
Typical Depths by Material
| Material | Typical Depth | 100 sq ft Needs |
|---|---|---|
| Mulch (beds) | 2–3 in | 17–25 ft³ (0.6–0.9 yd³) |
| Topsoil (lawns) | 4–6 in | 33–50 ft³ (1.2–1.9 yd³) |
| Concrete (slab) | 4 in | 33 ft³ (1.2 yd³) |
| Gravel (path) | 4–6 in | 33–50 ft³ (≈1.7–2.5 tons) |
| Sand (paver base) | 1 in | 8 ft³ (0.3 yd³) |
FAQ
How do I convert square feet to cubic feet?
Multiply sq ft by depth in feet: sq ft × (inches ÷ 12). A 100 sq ft bed at 3 in deep = 25 cu ft.
How many cubic yards is 100 sq ft at 3 inches?
25 cu ft ÷ 27 ≈ 0.93 cu yd — order 1 yard.
How many tons of gravel for 100 sq ft at 6 inches?
50 cu ft × ~100 lb/ft³ = 5,000 lb = 2.5 tons. Use the Gravel preset above for any area.
Does this work for concrete slabs?
Yes — use the Concrete 4" preset. A 20 × 20 ft slab (400 sq ft) at 4 in = 133 cu ft ≈ 4.9 cu yd; add 5–10% for spill and subgrade.
Sources
- Concrete ~150 lb/ft³ — Portland Cement Association (PCA) typical value for normal-weight concrete.
- Loose crushed stone ~100 lb/ft³, mulch ~25 lb/ft³, topsoil ~95 lb/ft³ — typical bulk densities published by aggregate suppliers and university cooperative extension services.
- Mulch depth 2–3 in — university cooperative extension recommendations for moisture retention without trunk rot.
- 1 cubic yard = 27 cubic feet; unit factors per NIST Special Publication 811.