How the concrete Calculator works
Slab volume is area times thickness, converted to cubic yards because that is how ready-mix trucks are ordered. An 80 lb bag yields about 0.60 cubic feet, so roughly 45 bags make a yard, and pros add about 10% waste for uneven subgrade and spillage.
yd³ = L × W × thickness(in)/12 ÷ 27, then × (1 + waste%)
Example: a 10 by 10 foot patio at 4 inches is 1.23 yards, or about 1.36 yards with 10% waste. That is 62 eighty-pound bags, which is exactly the point where calling a ready-mix truck starts making sense.
Frequently asked questions
Bags or a ready-mix truck?
Under about half a yard, bags are practical. Past one yard, mixing 45+ bags by hand is brutal and ready-mix delivers a stronger, more consistent pour, though short-load fees apply on small orders.
How thick should my slab be?
Four inches suits patios, walkways, and shed pads. Driveways for regular vehicles need five to six inches, plus reinforcement and a proper gravel base.
How many square feet does one yard of concrete cover?
81 square feet at 4 inches thick, 65 square feet at 5 inches, and 54 square feet at 6 inches.