How to use the cubic feet calculator
Choose a box (anything with square corners: a carton, a room, a truck bed, a freezer) or a cylinder (a tank, a drum, a round planter). Enter the measurements in whatever unit you used and set how many identical items you have. The total updates as you type.
The formulas
box: cubic feet = length × width × height (all in ft)
from inches: cubic feet = (L × W × H in inches) ÷ 1,728
cylinder: cubic feet = π × (diameter ÷ 2)² × height
Why 1,728? A cubic foot is 12 inches on each side, and 12 × 12 × 12 = 1,728 cubic inches.
Worked example: a 24 × 18 × 18 inch box
- Multiply in inches: 24 × 18 × 18 = 7,776 in³.
- Convert: 7,776 ÷ 1,728 = 4.5 ft³.
- That's 0.167 yd³, 127 litres or 33.7 US gallons.
Where people use cubic feet
| Job | What to measure |
|---|---|
| Moving and storage | Add up your boxes and furniture, then compare with the truck or unit's listed cubic feet. Leave 10-20% spare, because nothing packs perfectly. |
| Freezers and fridges | Inside dimensions. Listed capacity is usually a little less than the outside box. |
| Planters and raised beds | Inside length, width and soil depth. Bagged soil is sold by the cubic foot. |
| Concrete and mortar bags | The volume you need, then divide by the bag's yield, for example 0.60 ft³ for an 80 lb bag of concrete mix. |
| Rooms (HVAC, dehumidifiers) | Floor length × width × ceiling height. |
Other shapes
Most real objects are close to a box or a cylinder, but a few common shapes need their own formula:
- Cone or pile (a heap of mulch or gravel): π × radius² × height ÷ 3. A pile 6 ft across and 3 ft high is about 28 ft³, roughly one cubic yard.
- Wedge (a sloped fill or a ramp): length × width × height ÷ 2.
- Sphere: 4 ÷ 3 × π × radius³.
- Anything irregular: split it into boxes and cylinders, work out each, and add them up.
Tips and common mistakes
- Mixing feet and inches. 2 ft × 18 in × 18 in is not 648. Convert first, or use the unit boxes above.
- Outside vs inside. For capacity (how much fits in), measure inside. For shipping or storage space, measure outside.
- Irregular items. Measure the smallest box the item would fit into. That's the space it really takes up on a truck.
- Bags of soil or mulch list cubic feet on the front. Divide your total by the bag size and round up.
Questions people ask
How do you calculate cubic feet?
Multiply length × width × height, all in feet. If you measured in inches, multiply the three inch measurements and divide by 1,728. A box 24 × 18 × 18 inches is 7,776 cubic inches, or 4.5 cubic feet.
How many cubic feet is a moving box?
It varies by maker. Multiply the box's inside dimensions in inches and divide by 1,728. An 18 × 18 × 16 in box, a common medium size, is 3 cubic feet.
How do you find the cubic feet of a cylinder?
Multiply π (3.1416) by the radius squared by the height, all in feet. A tank 2 ft across and 4 ft tall has a radius of 1 ft, so its volume is 3.1416 × 1 × 4 = 12.6 cubic feet.
How many gallons are in a cubic foot?
7.48 US gallons, or 28.3 litres.
How many cubic feet are in a cubic yard?
27, because a cubic yard is 3 ft × 3 ft × 3 ft.
Sources and assumptions
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.