Cubic feet calculator
A box 4 ft long, 3 ft wide and 2 ft high holds 24 cubic feet, which is 0.89 cubic yards or 179.5 gallons.
The formula
Cubic feet = length (ft) × width (ft) × height (ft)
With every measurement in inches: length × width × height ÷ 1,728
4 ft × 3 ft × 2 ft = 24 cu ft
24 cu ft ÷ 27 = 0.89 cu yd
A cubic foot is 1,728 cubic inches, about 7.48 US gallons or 28.3 liters, and 27 cubic feet make a cubic yard. For a cylinder such as a tank or a round planter, the volume is π × (diameter ÷ 2)² × height.
Filling raised beds with bagged soil
Bagged soil and mulch are sold in cubic feet, so this is where cubic feet matter most. Bag counts are rounded up.
| Raised bed | Cu ft | Cu yd | 1 cu ft bags | 1.5 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|---|
| 2 × 4 ft, 10 in deep | 6.7 | 0.25 | 7 | 5 | 4 |
| 3 × 6 ft, 12 in deep | 18 | 0.67 | 18 | 12 | 9 |
| 4 × 4 ft, 12 in deep | 16 | 0.59 | 16 | 11 | 8 |
| 4 × 8 ft, 10 in deep | 26.7 | 0.99 | 27 | 18 | 14 |
| 4 × 8 ft, 12 in deep | 32 | 1.19 | 32 | 22 | 16 |
| 4 × 8 ft, 18 in deep | 48 | 1.78 | 48 | 32 | 24 |
| 4 × 12 ft, 12 in deep | 48 | 1.78 | 48 | 32 | 24 |
New soil settles after watering, so many gardeners fill a little over the top or top up after the first few weeks. Past about a cubic yard (27 cu ft), a bulk delivery usually costs less per yard than bags; the topsoil calculator works in yards.
Cubic feet in concrete and gravel
Concrete mix and bagged gravel are also labeled by cubic feet: an 80 lb bag of concrete mix makes about 0.6 cu ft, and a 50 lb bag of gravel or sand holds about 0.5 cu ft. Divide the cubic feet you need by the bag's yield and round up.