Concrete Calculator
Enter the size of a slab, footing or column and get the concrete volume in cubic yards and cubic meters, the number of 60 lb or 80 lb bags to buy, and how much the pour will weigh.
Bag counts include the waste allowance and round up to whole bags. Above about one cubic yard, ready-mix delivered by truck is usually cheaper than bags.
Formula and calculation
Worked example
A 10 ft × 10 ft slab, 4 in thick, is 100 × 0.333 = 33.33 cu ft of concrete — 1.2346 cu yd, or 0.9439 m³. In bags that is 59 80 lb bags or 78 60 lb bags, waste included, and the finished slab weighs about 5,000 lb.
Bags or a ready-mix truck?
One cubic yard is 27 cu ft, which takes 45 bags of 80 lb mix or 60 bags of 60 lb mix — well over 3,000 lb of material to carry, mix and place before it starts setting. Bags are the right call for footings, deck piers and small landings. For a driveway or a floor slab, ready-mix arrives already mixed, but you have minutes rather than hours to get it placed and finished. Most suppliers charge a short-load fee below 3–5 cu yd, so compare the delivered total, not the price per yard.
How thick should the slab be?
Four inches is the usual thickness for patios, walkways and shed floors. Driveways that carry cars are poured 5–6 in thick, usually with a thicker edge beam at the apron. Garage floors run 4–6 in, and anything a truck or heavy equipment drives on needs more plus reinforcement designed for the load. Local building codes set minimum thickness and reinforcement for driveways and slabs on grade, so check yours before you order.
What the results mean
- Volume
- The volume of the pour in cubic yards, the unit ready-mix concrete is sold in. One cubic yard is 27 cubic feet.
- Also
- The same volume in cubic meters, for metric quotes and drawings.
- Cubic feet
- The volume in cubic feet — the unit bag yields are measured in.
- Order this much
- The volume to actually order: the pour volume plus the waste allowance, in cubic yards.
- 80 lb bags
- The number of 80 lb bags to buy, rounded up to whole bags. Each bag mixes to about 0.60 cubic feet of concrete.
- 60 lb bags
- The number of 60 lb bags to buy, rounded up to whole bags. Each bag mixes to about 0.45 cubic feet of concrete.
- Weight
- How much the finished concrete weighs, using 150 lb per cubic foot for normal-weight concrete. Handy for checking formwork and truck limits.
Frequently asked questions
How many bags of concrete do I need for a slab?
Divide the volume in cubic feet by the yield of one bag. A cubic yard is 27 cu ft, so it takes 45 bags of 80 lb mix or 60 bags of 60 lb mix. Enter your slab dimensions above and the bag counts come out with the waste allowance already added.
How much extra concrete should I order?
Order 5–10% more than the calculated volume. An uneven subgrade, a trench dug a little deep and simple spillage all eat into the pour, and running short halfway through means a cold joint or a panicked second delivery. Set the waste allowance above and the volumes and bag counts follow.
How do I work out concrete for a round pier or sonotube?
Choose the column shape, tick the round box and enter the tube diameter as the width. A 10 in tube filled 4 ft high holds about 2.18 cu ft, so two of them take roughly 4.4 cu ft — about eight 80 lb bags with waste.
Does rebar or mesh change the concrete volume?
No. Reinforcement displaces a small amount of concrete rather than adding to it, and it does not change the volume this calculator reports. Your engineer or supplier specifies the bar size and spacing; the pour volume stays as calculated.