Concrete Calculator
Calculate how much concrete you need for slabs, driveways, and footings in cubic yards and bags.
How do I calculate cubic yards of concrete needed?
Formula: (Length x Width x Depth in feet) / 27 = Cubic yards. Convert depth from inches to feet first (divide by 12). Example: 20'x10' slab, 4" deep = 20 x 10 x (4/12) / 27 = 2.47 cubic yards. Always round up and add 5-10% extra for waste, spillage, and over-excavation. Concrete is sold by cubic yard (or fraction thereof) from ready-mix trucks.
How many bags of concrete do I need?
Bags needed depends on size: 80 lb bag = 0.6 cubic feet (45 bags per cubic yard), 60 lb bag = 0.45 cubic feet (60 bags per yard). Example: 2 cubic yards = 90 bags of 80 lb or 120 bags of 60 lb. Bags practical for small jobs (<1 yard). Larger projects use ready-mix trucks (cheaper, faster, better quality). Truck minimum usually 1 cubic yard, charges for partial loads.
What thickness should my concrete slab be?
Common thicknesses: Sidewalks/patios: 4 inches. Driveways/garage floors: 4-6 inches (6" for heavy vehicles). House slabs: 4-6 inches with proper base. Footings: 8-12 inches depending on load. Always use 4-6 inch gravel base for drainage and stability. Thicker isn't always better - proper base, rebar/mesh reinforcement, and expansion joints matter more than extra thickness for most residential applications.
Should I use rebar or wire mesh in my concrete?
Reinforcement prevents cracking: Wire mesh (6x6 WWF): Patios, sidewalks, 4" slabs - placed mid-height. Rebar (#3 or #4): Driveways, heavy-load areas, footings - typically 12-18" grid pattern. Fiber reinforcement: Mixed into concrete, good for crack control but not structural. For slabs over 10x10 feet or supporting vehicles, use reinforcement. Also critical: Control joints every 10 feet, proper curing, good base preparation.