Cubic yards, 80lb bags, and cost estimate
Enter your dimensions and this calculator returns the volume of concrete you need in cubic feet and cubic yards, the number of 80-pound bags of quikrete required for smaller pours, and a cost estimate based on your local ready-mix price. Slab mode handles patios, driveways, and shed pads; footing mode handles rectangular footings; column mode handles round sono-tubes and square posts.
A 10 ft × 10 ft slab at 4 inches thick: thickness = 4/12 = 0.333 ft, so volume = 10 × 10 × 0.333 = 33.3 ft³. That is 33.3 ÷ 27 = 1.23 yd³ (order 1.5 yd³ with 10% waste). In bags: 33.3 ÷ 0.6 = 56 eighty-pound bags. At $150/yd³, ready-mix costs about $185 — far easier than mixing 56 bags by hand.
How many 80lb bags of concrete make a yard? One cubic yard is 27 ft³ and each 80lb bag yields 0.6 ft³, so you'd need 45 bags per yard — mixing by hand beyond about 1 yard is impractical.
How thick should a concrete slab be? Patios and walkways: 4 inches. Driveways: 4–6 inches. Shed bases: 4–5 inches. Always check local code.
How much waste should I add? 5–10% for typical pours, up to 15% for irregular shapes or uneven ground.
60lb vs 80lb bags? A 60lb bag yields about 0.45 ft³. Multiply our bag count by 1.33 for 60lb bags.