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Concrete Slab Calculator
Estimate the concrete needed for a slab, footing, or pad. Enter the dimensions to get cubic yards, cubic feet, and how many pre-mix bags it takes.
How it's calculated
Volume = length × width × thickness. Thickness is converted from inches to feet, multiplied to get cubic feet, then divided by 27 for cubic yards. A 60-lb bag yields about 0.45 ft³ and an 80-lb bag about 0.60 ft³.
Order a little extra
Add roughly 5–10% for spillage, uneven subgrade, and waste. Above about half a cubic yard, ready-mix delivery is usually cheaper and easier than mixing bags.
Frequently asked questions
How many 80-lb bags of concrete are in a yard?
About 45 bags of 80-lb pre-mix make one cubic yard, since each yields ~0.60 ft³ and a yard is 27 ft³.
How thick should a concrete slab be?
Four inches is standard for patios and walkways; use 5–6 inches for driveways or areas with heavy loads.
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