Unit conversions: 1 CY = 27 ft³ = 0.7646 m³. To convert cubic feet to cubic yards, divide by 27. To convert m³ to CY, multiply by 1.30795. To convert CY to m³, multiply by 0.7646.
Volume math in CY: a 30 × 20 × 0.333 ft slab (30 × 20 ft footprint at 4 inches thick) equals 200 ft³, or 7.41 CY. Concrete is sold in 1/4 CY increments; round 7.41 up to 7.5 CY for ordering (add waste percentage first).
Density-derived mass: 1 CY of compacted earth at 1,660 kg/m³ weighs approximately 1.4 short tons. 1 CY of concrete at 2,400 kg/m³ weighs about 2.0 short tons. Tonnage matters for trucking capacity (a tandem dump holds 10-14 CY loose; a tri-axle 14-18 CY).