Work out concrete volume for slabs, footings, walls, and round columns. Enter dimensions to get cubic yards, feet, meters, bag counts, order quantity, and weight.
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Concrete volume is just length times width times thickness, converted into cubic yards, which is the unit ready-mix plants sell in. Enter your project shape and dimensions; the calculator computes the exact volume in cubic feet, cubic yards, and cubic meters. It then adds your waste allowance to give the quantity to order, converts that into premix bag counts for 40, 60, or 80 lb bags, and estimates the total weight of the pour at the standard 150 lb per cubic foot. Round columns and sonotubes use the cylinder formula, pi times radius squared times height.
Every concrete calculation comes down to one formula: cubic yards equals length in feet times width in feet times thickness in feet, all divided by 27, because a cubic yard is 27 cubic feet. Since thickness is usually measured in inches, divide it by 12 first. A handy shortcut: when length and width are in feet and thickness is in inches, yd3 = L × W × T / 324. For example, a 10x10 foot patio at 4 inches thick is 10 × 10 × 4 / 324 = 1.23 cubic yards. A 20x20 foot driveway at 4 inches is 4.94 cubic yards. For a round column, use pi × radius squared × height: a 12 inch diameter sonotube 4 feet deep holds about 3.14 cubic feet, or 0.12 cubic yards. The single biggest mistake is entering thickness in feet instead of inches, which inflates the answer twelvefold.
First pick the project shape: slab for patios, driveways, and shed bases; footing for continuous trench footings; wall for poured retaining or foundation walls; round column for sonotubes and deck piers. Enter the dimensions in feet for lengths and inches for thickness, which is how forms are usually measured. Set the waste allowance; 10 percent is the standard planning figure. Choose your premix bag size if you are mixing by hand, or ignore the bag count if a truck is delivering. The results give the exact volume in three units, the order quantity with waste included, the number of bags needed, and the total weight of the pour so you can plan the delivery.
Concrete is sold by the cubic yard in the United States, so cubic yards is the number you give the plant. One cubic yard equals 27 cubic feet, or 0.7646 cubic meters. A useful field fact about coverage: one cubic yard covers 81 square feet at 4 inches thick, 54 square feet at 6 inches, and about 65 square feet at 5 inches. Concrete yardage is simply the industry term for concrete volume expressed in cubic yards. The calculator shows all three volume units because some suppliers and metric plans quote cubic meters, and cubic feet is what you need when converting to bag counts. All three describe the same amount of concrete; only the packaging differs.
An 80 lb bag of premix yields about 0.60 cubic feet of concrete, a 60 lb bag yields 0.45, and a 40 lb bag yields 0.30. That means one cubic yard takes 45 bags of 80 lb mix, 60 bags of 60 lb, or 90 bags of 40 lb. For small jobs under about one cubic yard, bags are practical: you can mix in a wheelbarrow at your own pace. Above that, ready-mix delivery is usually cheaper per unit and far less labor. The crossover point is roughly half a yard to a yard. Watch out for the short-load fee: plants charge extra for deliveries below their posted minimum, often around 8 yards, so on small pours always ask the dispatcher about the minimum before choosing bags.
The raw formula gives the volume of a perfectly formed pour, and the field is never perfect. Always order about 10 percent more than the calculated volume. The extra covers subgrade variation, since a slab specified at 4 inches pours closer to 4.5 inches over a low spot; over-excavation on hand-dug footings; spillage and concrete left in the chute; and form deflection under the weight of wet concrete. After adding waste, round up to the nearest quarter yard for the order. Running short mid-pour is the expensive failure: a second delivery costs far more than the extra quarter yard, and a cold joint where the first pour set up is hard to repair.
Pick thickness by what the slab must carry. Patios, walkways, and shed bases are typically poured at 4 inches thick. Driveways and garage floors that carry vehicle weight should be 5 to 6 inches. Structural slabs, garage floors with heavy loads, and commercial work may call for 6 inches or more with rebar reinforcement. Footings are usually 8 to 12 inches deep, and must extend below the frost line in cold climates. When in doubt, the thicker end of the range is the safer choice; concrete is cheap compared to a cracked slab that must be replaced.
One cubic yard needs 45 bags of 80 lb premix, 60 bags of 60 lb premix, or 90 bags of 40 lb premix. This is because an 80 lb bag yields 0.60 cubic feet and a yard is 27 cubic feet. These figures come from the bag yields printed on standard premix, and they assume no waste; add 10 percent to be safe.
A 10x10 foot slab at 4 inches thick is 10 × 10 × 4 / 324 = 1.23 cubic yards, or 33.3 cubic feet. With a 10 percent waste allowance, order about 1.36 cubic yards. In bags that is roughly 62 bags of 80 lb mix, so this size sits right at the crossover where ready-mix delivery becomes practical.
Multiply length in feet by width in feet by thickness in feet, then divide by 27. If thickness is in inches, use the shortcut: cubic yards = length × width × thickness in inches / 324. For a round column, use pi × (diameter in inches / 24) squared × height in feet, then divide by 27.
Yes, order about 10 percent more than the calculated volume. Subgrades are never perfectly flat, forms bow, and some concrete stays in the truck or wheelbarrow. Running short on an active pour is far more expensive than a little leftover concrete: it risks a cold joint and a second delivery with a short-load fee.
A short-load fee is a charge ready-mix plants add to deliveries below their posted minimum, which is commonly around 8 cubic yards. The fee can be steep compared to the price of the extra concrete itself, which is why rounding your order up is almost always cheaper than ordering to the exact calculated number on a small pour.
Bagged premix wins for small jobs under about half a cubic yard, since you avoid truck minimums and fees. Above roughly one cubic yard, ready-mix delivery is cheaper per unit and much faster, with a more consistent mix. Do the math both ways: a full yard is already 45 bags of 80 lb mix, or 3,600 lb of dry material to lift and mix by hand.
Normal-weight concrete weighs 140 to 155 lb per cubic foot, typically 150. One cubic yard therefore weighs about 4,050 lb, roughly 2 tons. The calculator estimates your pour's weight at 150 lb per cubic foot so you can plan trailer loads and check what the ground or forms must support.
Use the footing shape: length in feet times width in feet times depth in feet, divided by 27. For example, 120 linear feet of footing 16 inches wide and 8 inches deep is 120 × (16/12) × (8/12) = 106.7 cubic feet = 3.95 cubic yards. Hand-dug trenches over-excavate, so use a 10 percent waste allowance and measure the real width in a few places.