Cubic feet are length × width × depth with every measurement in feet. A box 10 ft long, 4 ft wide and 6 in deep holds 10 × 4 × 0.5 = 20 cubic feet, which is 0.741 cubic yards, 566 liters or 149.6 US gallons. When one measurement is in inches, divide it by 12 before you multiply; the calculator does that for any mix of feet, inches, yards, centimeters and meters.
How cubic feet are calculated
Cubic feet = length (ft) × width (ft) × depth (ft)
Each dimension is converted to feet first: inches ÷ 12, yards × 3, meters × 3.2808, centimeters ÷ 30.48. Then the three are multiplied. From there, NIST Handbook 44 fixes every other unit exactly: 1 cubic foot is 1,728 cubic inches, 27 cubic feet make a cubic yard, and a US gallon is 231 cubic inches, so one cubic foot holds 7.48 gallons.
Worked example
The calculator opens with 10 ft × 4 ft × 6 in:
- Depth in feet: 6 ÷ 12 = 0.5 ft
- Volume: 10 × 4 × 0.5 = 20 cu ft
- Cubic yards: 20 ÷ 27 = 0.741 cu yd
- Cubic meters: 20 × 0.0283168 = 0.566 m³
- Gallons: 20 × 7.48052 = 149.6 gal
Change "How many" to count identical boxes, forms or beds: five of them are 100 cu ft.
Cubic feet calculator for a cylinder
Round things use π × radius² × height. Measure the diameter straight across and halve it for the radius. A post hole or tube form 12 in across and 4 ft deep is π × 0.5² × 4 = 3.14 cubic feet, or 23.5 gallons. A 30 in wide, 3 ft tall rain barrel works out to π × 1.25² × 3 = 14.7 cu ft, about 110 gallons. Filling tube forms with concrete is its own job, handled with bag counts in the sonotube concrete calculator.
Cubic feet from square feet
If you already know the area, multiply it by the depth in feet. A 40 sq ft area at 6 in deep is 40 × 0.5 = 20 cu ft, the same as the box above. The square footage calculator gives the area of odd shapes first, and then "Area × depth" here turns it into volume.
Cubic feet with inches in every dimension
Small boxes are usually measured in inches. Multiply the three and divide by 1,728: a moving box 18 × 18 × 16 in is 5,184 ÷ 1,728 = 3 cu ft. The calculator does the same if you set all three units to inches. For how many boxes a move takes, the moving box calculator counts them by home size.
Mixed units in one box
Tape measures in the US read feet and inches, product labels read cubic feet, and European appliances list liters. Enter each side in the unit you actually measured it in: 2 m × 90 cm × 15 in is fine. The worked math shows each value as you typed it and the result in every unit, so you can check the step that matters.
Conversion table
| From | Cubic feet | Cubic yards | Cubic meters | Liters | US gallons |
|---|---|---|---|---|---|
| 1 cubic foot | 1 | 0.03704 | 0.02832 | 28.317 | 7.481 |
| 1 cubic yard | 27 | 1 | 0.7646 | 764.555 | 201.974 |
| 1 cubic meter | 35.315 | 1.308 | 1 | 1,000 | 264.172 |
| 1 US gallon | 0.13368 | 0.00495 | 0.003785 | 3.785 | 1 |
| 1 liter | 0.03531 | 0.00131 | 0.001 | 1 | 0.26417 |
The values come from the exact definitions in NIST Handbook 44, Appendix C.
Common questions after cubic feet
How many cubic feet in a cubic yard? 27, because a yard is 3 ft and 3 × 3 × 3 = 27. Bulk materials are sold by the yard, so the cubic yard calculator starts from yards.
How many cubic feet of concrete do I need? Measure the form and work out the cubic feet here, or go straight to the concrete calculator, which turns the volume into bags.
How do I measure a freezer, a trunk or a storage unit? Measure the inside, not the outside: walls and insulation take several inches off each side. A storage unit sold as 10 × 10 with an 8 ft ceiling holds 800 cu ft of space, but you will stack boxes to maybe 6 ft, which is 600 cu ft you can use.
Why does my bag say 2 cu ft when the box I fill looks bigger? Loose materials settle. Buy by the volume you calculate and keep a bag spare for topping up.
More measuring tools are in the measuring and planning calculators.