Sqft to Cubic Feet Calculator
Square feet measure area; cubic feet measure volume. Add a depth and this converts between them.
To convert square feet to cubic feet, multiply the area by the depth in feet. For 200 sq ft at 4 inches deep: 4 ÷ 12 = 0.333 ft, and 200 × 0.333 = 66.7 cubic feet. Enter the depth in inches below and the conversion is automatic.
Concrete is ordered in cubic yards — 27 cubic feet to the yard. Bag counts assume 0.45 ft³ per 60 lb bag and 0.6 ft³ per 80 lb bag.
The formula
Cubic feet = Square feet × Depth in feet
The only trap is the depth, which is nearly always quoted in inches while the area is in feet. Divide the inches by 12 first:
- 2 inches = 0.167 ft
- 4 inches = 0.333 ft
- 6 inches = 0.5 ft
So a 400 sq ft patio poured 4 inches thick needs 400 × 0.333 = 133.3 cubic feet, which is 133.3 ÷ 27 = 4.94 cubic yards of concrete.
Why concrete is ordered in cubic yards
Ready-mix concrete is sold by the cubic yard, and one cubic yard is 27 cubic feet (3 × 3 × 3). Divide your cubic feet by 27 to get the order quantity.
Suppliers generally have a minimum order and charge for a partial load, so most contractors round up and add 5–10% for spillage and uneven subgrade. On the 4.94 yard example above you would order 5.5 yards.
Typical depths by material
If you are not sure what depth to use, these are the usual figures:
- Concrete patio or walkway — 4 inches
- Concrete driveway — 5 to 6 inches
- Garden mulch — 2 to 3 inches
- Topsoil for a new lawn — 4 to 6 inches
- Gravel driveway base — 4 to 6 inches
- Paver sand bedding — 1 inch
Cubic feet by area and depth
| Area | 2 in deep | 4 in deep | 6 in deep |
|---|---|---|---|
| 100 sq ft | 16.7 ft³ | 33.3 ft³ | 50 ft³ |
| 200 sq ft | 33.3 ft³ | 66.7 ft³ | 100 ft³ |
| 400 sq ft | 66.7 ft³ | 133.3 ft³ | 200 ft³ |
| 600 sq ft | 100 ft³ | 200 ft³ | 300 ft³ |
| 1,000 sq ft | 166.7 ft³ | 333.3 ft³ | 500 ft³ |
Frequently asked questions
How do I convert sqft to cft?
Multiply the square footage by the depth in feet. For 200 square feet at 6 inches deep: 6 ÷ 12 = 0.5 ft, so 200 × 0.5 = 100 cubic feet.
How many cubic feet are in a cubic yard?
There are 27 cubic feet in one cubic yard, because a cubic yard is 3 ft × 3 ft × 3 ft.
How much concrete do I need for a 400 sq ft patio?
At the standard 4 inch thickness, 400 sq ft needs 133.3 cubic feet, which is 4.94 cubic yards. Order about 5.5 yards to allow for spillage and an uneven base.
Can I convert square feet to cubic feet without a depth?
No. Square feet measure a flat area and cubic feet measure volume, so a third dimension is required. Without a depth or thickness there is no conversion to make.
How many bags of concrete do I need per cubic foot?
An 80 lb bag of premixed concrete yields about 0.6 cubic feet, and a 60 lb bag about 0.45 cubic feet. So one cubic foot needs roughly 1.7 of the 80 lb bags.