Math & Science · Guide
Square Feet to Cubic Feet and Cubic Yards
Square feet measure a surface. Cubic feet measure a space. The missing piece is always depth.
Want the answer for your own numbers? Use the free Area Calculator — it does every step below for you.
Why you cannot convert directly
Square feet (ft²) measure flat area — a floor, a lawn, a wall. Cubic feet (ft³ or CFT) measure volume — how much fills a space. They are different kinds of measurement, so you need one more number: the depth (or height, or thickness).
Square feet to cubic feet
Cubic feet = square feet × depth in feet
Depth in inches? Divide by 12 first. 4 inches = 0.333 ft; 6 inches = 0.5 ft.
Example: gravel for a 200 ft² path, 3 inches deep
3 ÷ 12 = 0.25 ft. 200 × 0.25 = 50.
50 cubic feet
Cubic feet to square feet
Run it backwards: divide by the depth.
Square feet = cubic feet ÷ depth in feet
A 2 ft³ bag of mulch spread 3 inches (0.25 ft) deep covers 2 ÷ 0.25 = 8 square feet. Spread 2 inches deep, it covers 12 ft².
Square feet to cubic yards
Bulk soil, mulch, gravel and concrete are sold by the cubic yard. One cubic yard = 27 cubic feet (3 × 3 × 3).
Cubic yards = square feet × depth in feet ÷ 27
| Area | 2 in deep | 3 in deep | 4 in deep | 6 in deep |
|---|---|---|---|---|
| 100 ft² | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ | 1.85 yd³ |
| 250 ft² | 1.54 yd³ | 2.31 yd³ | 3.09 yd³ | 4.63 yd³ |
| 500 ft² | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ | 9.26 yd³ |
| 1,000 ft² | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ | 18.52 yd³ |
Cubic yards to square feet (coverage)
One cubic yard covers:
- 324 ft² at 1 inch deep
- 162 ft² at 2 inches
- 108 ft² at 3 inches
- 81 ft² at 4 inches
- 54 ft² at 6 inches
Worked example: a concrete slab
A 10 ft × 12 ft patio, 4 inches thick
Area: 10 × 12 = 120 ft². Depth: 4 ÷ 12 = 0.333 ft.
Volume: 120 × 0.333 = 40 ft³. In cubic yards: 40 ÷ 27 = 1.48 yd³.
Add 10% for waste: 1.63 yd³.
Order about 1.6 cubic yards of ready-mix
Mixing it yourself from bags? An 80 lb bag of concrete mix makes about 0.6 ft³, and a 60 lb bag about 0.45 ft³. So 40 ft³ needs about 67 bags of 80 lb — around 74 with 10% extra. At that size, ready-mix is usually easier.
Bags of mulch or soil
Garden products are often sold in 2 ft³ bags. One cubic yard equals 13.5 of those bags. A 200 ft² bed at 3 inches deep needs 50 ft³ — that is 25 bags of 2 ft³, or just under 2 cubic yards in bulk.
Irregular and round areas
Split an odd shape into rectangles, triangles and circles, find each area, and add them up. A round flower bed with a 4 ft radius has an area of π × 4² = 50.3 ft². At 3 inches deep it needs 50.3 × 0.25 = 12.6 ft³ of mulch.
Typical depths
| Material | Common depth |
|---|---|
| Mulch | 2–3 inches |
| Gravel path | 2–4 inches |
| Topsoil for new lawn | 4–6 inches |
| Concrete patio or shed base | 4 inches |
| Concrete driveway | 4–6 inches |
Check your supplier’s advice for your soil and load — a driveway for heavy vehicles may need more.
Metric: square metres to cubic metres
Same idea: cubic metres = square metres × depth in metres. A 20 m² slab 10 cm (0.1 m) thick needs 2 m³ of concrete. To convert cubic metres to cubic feet (CFT), multiply by 35.315 — the cubic meter calculator does both.
Order a little extra
Add 5–10% for concrete (spillage, uneven ground) and about 10% for mulch and soil, which settle. Measure the area with the area calculator first, then multiply by depth.
Frequently asked questions
Multiply the square footage by the depth in feet. 200 square feet at 3 inches (0.25 ft) deep is 50 cubic feet. Convert inches to feet by dividing by 12.
It depends on depth: about 324 square feet at 1 inch, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches.
At 4 inches thick, a 10 ft × 10 ft slab is 33.3 cubic feet. With 80 lb bags making about 0.6 cubic feet each, that is about 56 bags, or around 61 with 10% extra for waste.
27. A cubic yard is 3 feet × 3 feet × 3 feet. To turn cubic feet into cubic yards, divide by 27; to go the other way, multiply by 27.