Length times width times height
The volume of any box is its three sides multiplied together. The catch is units: they all have to be feet before you multiply. Measure in feet and you get cubic feet directly.
Measuring in inches instead
If your tape gives inches, either divide each side by 12 first, or multiply the three inch measurements and divide the result by 1,728. Both give the same answer; 1,728 is just 12 × 12 × 12, the number of cubic inches in a cubic foot.
- Don’t mix the two. A 24 × 18 × 18 box in inches is 4.5 ft³, but read as feet it would be 7,776 ft³. Convert every side to the same unit first.
- Divide by 1,728, not 12. The 12-per-foot ratio is for length; volume cubes it, so the divisor is 12³.
Box size reference and unit values
| Box (inches) | Cubic feet |
|---|---|
| 12 × 12 × 12 | 1.0 ft³ |
| 18 × 18 × 16 | 3.0 ft³ |
| 24 × 18 × 18 | 4.5 ft³ |
| 24 × 24 × 24 | 8.0 ft³ |
Each cubic foot is about 28.3 litres, 7.48 US gallons or 0.0283 m³. There are 27 cubic feet in a cubic yard.
Common questions
How do I calculate the cubic feet of a box?
Multiply length by width by height, with all three in feet. For a 2 ft by 1.5 ft by 1 ft box that is 3 cubic feet.
How do I get cubic feet from inches?
Multiply the three sides in inches, then divide by 1,728 (that is 12 cubed). A 36 by 24 by 24 inch box is 20,736 cubic inches, which is 12 cubic feet.
How many gallons is a cubic foot?
About 7.48 US gallons per cubic foot, or 6.23 imperial gallons. So a 4 cubic foot box holds roughly 30 US gallons.
