Concrete Calculator
Estimate concrete for slabs, footings, and pads — in cubic yards and bags.
Enter your slab dimensions and thickness to get the concrete volume in cubic yards and cubic feet, plus how many 40, 60, or 80-lb bags you'd need. A small waste allowance is included by default to cover spillage and uneven subgrade.
How it works
Volume is length × width × thickness (converted to feet), divided by 27 to get cubic yards. Bag counts use standard yields: an 80-lb bag makes about 0.60 cubic feet, a 60-lb bag about 0.45, and a 40-lb bag about 0.30. For large pours, ready-mix delivery by the cubic yard is usually cheaper than bags.
Frequently asked questions
How much concrete do I need?
Multiply the slab's length, width, and thickness (in feet) and divide by 27 for cubic yards. A 10 ft × 10 ft slab at 4 inches thick is about 1.23 cubic yards before waste.
How many 80-lb bags of concrete are in a cubic yard?
About 45 bags. An 80-lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 ≈ 45 bags.
Should I add extra concrete for waste?
Yes — a 5–10% allowance is standard to cover spillage, uneven ground, and over-excavation. The calculator includes 5% by default, which you can change.
How much does a yard of concrete weigh?
About 3,700 pounds (roughly 1.85 tons) per cubic yard for standard mix — nearly two tons, which is why large pours come by truck.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.