Concrete Calculator
How many yards or bags of concrete does your slab, footing, or post hole need?
How this is calculated
- Volume in cubic feet = length × width × (depth ÷ 12)
- Cubic yards = cubic feet ÷ 27
- Order amount = cubic yards × (1 + waste % ÷ 100)
- Bags = ⌈order amount × 27 ÷ bag yield⌉, where an 80 lb bag yields 0.60 cu ft, a 60 lb bag 0.45 cu ft, and a 40 lb bag 0.30 cu ft of mixed concrete.
Common questions
How many 80 lb bags of concrete are in a cubic yard?
One cubic yard equals 27 cubic feet, and an 80 lb bag yields about 0.60 cu ft of mixed concrete — so it takes about 45 eighty-pound bags to make one full cubic yard. At that point a ready-mix delivery is usually cheaper and far less labor.
How much concrete do I need for a 10×10 slab?
A 10 ft × 10 ft slab at the standard 4-inch patio depth is about 1.23 cubic yards. With a 10% waste allowance you should order 1.36 cubic yards — roughly 62 eighty-pound bags if you are mixing by hand.
Should I order extra concrete?
Yes. Add about 10% for spillage, over-digging, and uneven subgrade. Running short mid-pour is the single most expensive mistake in concrete work — a second small delivery or a store run costs disproportionately more than ordering slightly extra the first time.
Bags or a ready-mix truck — which should I use?
Rule of thumb: under about 1 cubic yard (~45 eighty-pound bags), bags mixed on-site are practical. Above that, ready-mix delivered in a truck saves hours of mixing and usually money. Concrete begins setting 30–60 minutes after mixing, so plan the pour before anything is ordered.
How thick should a concrete slab be?
Patios, walkways, and shed pads: 4 inches. Residential driveways: 5–6 inches over a compacted gravel base. Footings follow local code — typically 12 inches deep minimum, but check your jurisdiction before pouring.