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Concrete Calculator
Find out how much concrete you need for a slab, patio, footing or post hole, in cubic yards and in bags, with the cost.
YOU NEED
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Estimate only. Bag yields, material density and waste vary by product and supplier. Confirm quantities with your supplier and check local building codes before you buy or build.
How to calculate concrete
Multiply length × width × thickness, all in feet, to get cubic feet, then divide by 27 for cubic yards. A 12 × 10 ft slab 4 inches thick is 40 cubic feet. With 10% extra for waste and uneven ground, order about 44 cubic feet, or 1.63 cubic yards.
How many bags of concrete do I need?
Divide your volume by what one bag yields. An 80 lb bag makes about 0.6 cubic feet, a 60 lb bag 0.45, a 50 lb bag 0.375 and a 40 lb bag 0.3. A cubic yard takes about 45 bags of 80 lb. In Canada a 30 kg bag yields about 0.5 cubic feet and a 25 kg bag about 0.41.
How much does concrete weigh?
Normal concrete weighs about 150 pounds per cubic foot, or roughly 4,050 pounds (2 US tons) per cubic yard. The calculator shows the weight of your pour, which helps when planning a delivery, a wheelbarrow load or the load on a deck or a trailer.
Bags or ready-mix?
Bags are practical up to roughly one cubic yard, about 45 bags of 80 lb. Beyond that, mixing by hand is slow and a ready-mix truck is usually cheaper. Many plants have a minimum load, so compare both prices using the cost boxes above.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45. One cubic yard is 27 cubic feet and an 80 lb bag yields about 0.6 cubic feet. It takes about 60 bags of 60 lb or 90 bags of 40 lb.
How much concrete do I need for a 10 x 10 slab?
At 4 inches thick a 10 × 10 ft slab is 33.3 cubic feet, 1.23 cubic yards. With 10% waste that is about 1.36 cubic yards, or 62 bags of 80 lb.
How much does a cubic yard of concrete weigh?
About 4,050 pounds, or 2 US tons. A 12 × 10 ft slab 4 inches thick with 10% waste is 1.63 cubic yards, roughly 6,600 pounds of concrete.
How much extra concrete should I order?
Order 5 to 10% extra for spillage, uneven subgrade and forms that settle. It is cheaper than a second delivery or running short mid-pour.
How thick should a concrete slab be?
Patios, walkways and shed pads are usually 4 inches thick. Driveways and garage floors are often 5 to 6 inches. Check your local building codes and supplier.
How do I calculate concrete for a round hole or column?
Pick circle and enter the diameter as the length. Volume is π × radius² × depth. A 12 inch hole 36 inches deep needs about 2.4 cubic feet, roughly 4 bags of 80 lb.
How accurate is this estimate?
It is a planning estimate, not an order. Bag yields, material density and waste vary by product, supplier and job, so confirm quantities with your supplier and check local building codes before you buy or pour.
Are my measurements saved?
No. Everything is calculated in your browser. Nothing is uploaded or stored.
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Also on this topic: Concrete pad and slab calculator, Concrete slab cost calculator.