A cubic foot is the volume of a cube that measures one foot along each edge. Because a foot is 12 inches, a cubic foot is 12 × 12 × 12 = 1,728 cubic inches. NIST gives it as 0.02831685 m³, which is 28.317 liters.
Formula
volume (ft³) = length (ft) × width (ft) × height (ft)
m³ = ft³ × 0.02831685
ft³ = yd³ × 27
Example
A box 3 ft long, 2 ft wide and 1.5 ft high holds 3 × 2 × 1.5 = 9 ft³, which is 9 × 28.3168 = 254.9 L. It equals 9 ÷ 27 = 0.333 cubic yards.
Common mistakes
Cubic units scale with the cube of the length: 3 feet make a yard, but 3 × 3 × 3 = 27 cubic feet make a cubic yard. Mixing feet and inches in one product (for example 2 ft × 6 in × 3 ft) also gives wrong results; convert to one unit first. Use the cubic feet calculator for rooms, boxes and bags, and how many inches in a foot for the length step.