The cubic feet formula
cubic feet = length (ft) × width (ft) × height (ft)
For anything that is not a box, find the area of the flat face in square feet and multiply by the height or depth:
| Shape | Cubic feet | Example |
|---|---|---|
| Box or room | length × width × height | 6 × 4 × 3 = 72 |
| Cylinder (tank, round hole, tube) | 3.1416 × radius² × height | 2 ft across, 4 ft tall: 12.6 |
| Triangular prism | base × height ÷ 2 × length | 4 ft base, 3 ft high, 10 ft long: 60 |
| Several identical items | one item × how many | 6 boxes of 3 cu ft: 18 |
The calculator does the same thing: pick the shape, enter sizes in whatever units you measured, and use “How many” for repeats. Add a section for each extra piece; it totals them.
Converting other units to feet first
| Measured in | To get feet | Example |
|---|---|---|
| Inches | ÷ 12 | 30 in = 2.5 ft |
| Yards | × 3 | 2 yd = 6 ft |
| Centimeters | ÷ 30.48 | 90 cm = 2.95 ft |
| Meters | × 3.2808 | 2 m = 6.56 ft |
If all three measurements are in inches, there is a shortcut: multiply them and divide by 1,728, the number of cubic inches in a cubic foot.
Worked examples
A shipping box, 24 × 18 × 18 inches. 24 × 18 × 18 = 7,776 cubic inches. 7,776 ÷ 1,728 = 4.5 cubic feet.
A room, 12 ft × 10 ft with an 8 ft ceiling. 12 × 10 × 8 = 960 cubic feet, or 35.6 cubic yards. Room volume like this is what fan, dehumidifier and air-purifier ratings are often based on.
A storage unit, 10 × 10 ft and 8 ft high. 10 × 10 × 8 = 800 cubic feet.
A round water tank, 3 ft across and 4 ft tall. Radius 1.5 ft: 3.1416 × 1.5 × 1.5 × 4 = 28.3 cubic feet, which is about 28.3 × 7.48 = 212 gallons.
A trench, 20 ft long, 18 in wide, 2 ft deep. 18 in = 1.5 ft. 20 × 1.5 × 2 = 60 cubic feet, or 2.22 cubic yards.
Cubic feet to other units
| 1 cubic foot equals | Value |
|---|---|
| Cubic inches | 1,728 |
| Cubic yards | 0.037 (1 ÷ 27) |
| Cubic meters | 0.0283 |
| Liters | 28.32 |
| US gallons | 7.48 |
To go from cubic feet to cubic yards for an order, use the cubic feet to cubic yards converter. For metric, see cubic meters to cubic yards.
Weight of a cubic foot
Handy when you need to know whether a load is safe to lift or carry. These are typical figures; moisture and mix change them.
| Material | About this much per cubic foot |
|---|---|
| Water | 62.4 lb |
| Concrete | 145 to 150 lb |
| Asphalt (compacted) | about 145 lb |
| Gravel | about 100 to 105 lb |
| Sand (dry) | about 100 lb |
| Topsoil | about 75 lb, more when wet |
| Mulch | about 15 to 30 lb |
Pick a material in the calculator to see the total weight in tons, or use the cubic yards to tons converter.
For storage and moving, the usable space is less than the measured volume because of shelves, gaps and odd-shaped items. For tanks, the calculator gives the full volume; fill levels are usually below the top.
Questions people ask
- How do you calculate cubic feet?
- Multiply length × width × height, all in feet. A box 6 ft long, 4 ft wide and 3 ft high is 6 × 4 × 3 = 72 cubic feet.
- How do I get cubic feet from inches?
- Multiply the three measurements in inches, then divide by 1,728 (12 × 12 × 12). A box 24 × 18 × 12 in is 5,184 cubic inches, which is 3 cubic feet.
- How do I find the cubic feet of a cylinder?
- 3.1416 × radius × radius × height, with everything in feet. A tank 2 ft across and 4 ft tall is 3.1416 × 1 × 1 × 4 = 12.6 cubic feet.
- How many gallons are in a cubic foot?
- About 7.48 US gallons. Multiply cubic feet by 7.48 to estimate how much water a tank or pool holds.
- How many cubic feet are in a cubic yard?
- 27. Divide cubic feet by 27 to get cubic yards.