A cubic yard is a unit of volume equal to a cube measuring 3 ft × 3 ft × 3 ft. That's 27 cubic feet, or roughly 202 gallons. One cubic yard of concrete weighs about 4,050 lb (about 2 tons).
In terms of coverage, one cubic yard of concrete will fill: • 81 sq ft at 4 inches deep (standard patio or sidewalk) • 54 sq ft at 6 inches deep (standard driveway) • 162 sq ft at 2 inches deep (overlay or topping)
If you're working in bags instead of ready-mix, one cubic yard equals about 60 bags of 80 lb concrete mix, or 90 bags of 60 lb mix.