Concrete Calculator

The rough crossover is 1 to 1.5 cubic yards. Below that, bags win on cost and logistics. Above it, consider that a yard is about 45 eighty-pound bags — mixing that by hand is a brutal day and the concrete at the start of the pour is setting before you finish. Trucks have minimum-load and short-load fees; ask when you call.

4 inches is the standard for patios, walkways, and shed pads. Driveways and anything carrying vehicles want 5–6 inches. Thickness is where under-ordering hides: a '4 inch' slab poured over an uneven base often averages 4.5 inches or more, which is exactly what the waste margin is for.

Because the ground isn't a machined surface. Low spots in the subgrade, forms that bow slightly, spillage, and the bit left in the mixer all consume concrete the geometry doesn't predict. 5–10% is standard practice; running out mid-pour creates a cold joint — a visible, structurally weaker seam.

A cubic yard is 27 cubic feet, so roughly 45 bags at 80 lb (0.60 cu ft each), 60 bags at 60 lb (0.45), or 90 bags at 40 lb (0.30). Seeing those counts is usually what convinces people the truck is worth it for bigger pours.