Concrete Calculator
Enter your slab dimensions to get the volume in cubic yards and cubic meters, the number of 60 lb or 80 lb bags, the weight, and an estimated cost.
Bag yields used: 80 lb = 0.60 ft³ (0.0170 m³), 60 lb = 0.45 ft³ (0.0127 m³). Pre-mixed bag performance varies by brand and by how much water you add — always check the bag label. For pours over about 1 yd³, ready-mix delivery is usually the practical choice.
Frequently asked questions
How much concrete do I need for a slab?
Volume = length × width × thickness, all in the same unit. For a 10 ft × 12 ft slab 4 inches thick: 10 × 12 × (4 ÷ 12) = 40 cubic feet. Divide by 27 to get cubic yards — about 1.48 yd³. Always add 5–10% for spillage, uneven subgrade and thickness variation; running short mid-pour is far worse than having a wheelbarrow left over.
How many 80 lb bags make a cubic yard?
An 80 lb bag of pre-mixed concrete yields about 0.60 cubic feet, so one cubic yard (27 ft³) needs roughly 45 bags. A 60 lb bag yields about 0.45 ft³, so about 60 bags per yard. For anything above roughly one cubic yard, ready-mix delivery is usually cheaper and much less work than hauling bags.
What thickness should a concrete slab be?
Common practice in the US: 4 inches for footpaths, patios and shed floors; 5–6 inches for driveways carrying cars; 6 inches or more with rebar for heavy vehicles or RV pads. Thicker slabs also need more control joints — typically every 8–12 feet in both directions to limit cracking.
How much does a yard of concrete weigh?
About 4,050 lb (roughly 1,840 kg), or close to 2 tons per cubic yard. That matters for two reasons: delivery trucks carry a limited load, and if you are mixing by hand you cannot move a yard of concrete in a single batch — plan on multiple mixes and a helper.