How it works
Cubic feet = Length × Width × (Depth ÷ 12) · Cubic yards = Cubic feet ÷ 27. Base gravel weighs roughly 1.35 tons per cubic yard; a 4-inch base is typical for patios (6 in for driveways).
Example
A 10 × 10 ft patio with a 4 in base is about 1.2 cubic yards (~1.7 tons).