Concrete Estimator
Enter the size of your job to get cubic yards, cubic meters and bags needed.
Concrete calculator for each job
How to use the concrete estimator
- Choose from these shapes: slab, footing, wall, round column or steps. Think of a slab as a flat floor, such as a patio. A footing is the concrete base beneath a wall or post.
- Type in your sizes. For a size of 12 ft 6 in, enter 12'6" (the ' sign means feet and the " sign means inches). If the measurement is 3½ in, enter 3 1/2.
- Check the cubic yards and bags. Because the extra for spills and uneven ground that you chose is already included, buy that amount.
How the concrete estimator works
You have two choices: prepare concrete yourself with bags, or order ready-mix, which a plant prepares and a truck delivers. One cubic yard fills a cube with 3-foot sides (27 cubic feet). You can buy ready-mix concrete by the cubic yard. Your measurements are first converted to cubic feet. Next, the extra amount you selected for spills and uneven ground gets added. You’ll see complete bags, cubic yards and cubic meters, with cubic meters being the metric unit.
Concrete volume formula
Provide your measurements, and the tool calculates the amount you need to buy. Include 10% for spills and uneven ground. For a patio that measures 10 ft by 10 ft and is 4 in thick, you need 1.36 cubic yards, rather than 1.23.
See the formula
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. The number 12 changes inches into feet, and 27 changes cubic feet into cubic yards, since one cubic yard fits 27 cubic feet. With a round column, the tool calculates the circle's area using the width measured straight across.
How many bags of concrete per cubic yard
A larger bag makes more concrete, which means you need fewer bags. A cubic yard requires 45 big 80 lb bags or 90 small 40 lb bags. These figures come from Quikrete and Sakrete, two big US brands of bagged concrete. Every size appears in the table. When your amount is under a full bag, the tool still counts one whole bag, so you don't come up short.
| Bag | Makes (cubic feet) | Makes (liters) | Bags for one cubic yard | Bags for one cubic meter |
|---|---|---|---|---|
| 40 lb (18.1 kg) | 0.30 | 8.5 | 90 | 117.7 |
| 50 lb (22.6 kg) | 0.375 | 10.6 | 72 | 94.2 |
| 60 lb (27.2 kg) | 0.45 | 12.7 | 60 | 78.5 |
| 80 lb (36.2 kg) | 0.60 | 17.0 | 45 | 58.9 |
Concrete estimator FAQ
How do I calculate how much concrete I need?
Multiply length, width and thickness in feet to find the cubic feet. To find cubic yards, divide that result by 27. Measured at 10 by 10 feet and 4 inches thick, a slab holds 33.3 cubic feet, which comes to 1.23 cubic yards. Add another 5 to 10 percent before you order, to cover spills and uneven ground.
How much concrete do I need for a 10x10 slab?
You need 1.23 cubic yards of concrete for a slab that measures 10 feet by 10 feet and is 4 inches thick. The total becomes about 1.36 cubic yards when you add 10 percent for spills and uneven ground. The big 80 lb size requires about 62 bags. With lighter bags, the counts rise: at 60 lb you need 82 bags, at 50 lb 98, and at 40 lb 123. At 6 inches thick, that slab takes 1.85 cubic yards.
How many 80 lb bags of concrete are in a cubic yard?
45. Once mixed, an 80 lb bag of concrete provides about 0.60 cubic feet (the number Quikrete and Sakrete both list). Therefore, 45 bags fill a cubic yard, which is 27 cubic feet.
How many cubic feet are in a 60 lb or 50 lb bag of concrete?
A 60 lb bag provides about 0.45 cubic feet, while a 50 lb bag provides about 0.375 cubic feet. Filling a cubic yard requires 60 bags at 60 lb or 72 bags at 50 lb. Each 40 lb bag produces 0.30 cubic feet, while 90 bags fill a yard.
How thick should a concrete slab be?
A patio, walkway or shed floor usually has a thickness of 4 inches. A 5 to 6 inch thickness is needed on driveways and garage floors for cars and trucks. Bagged mix works for a slab that's 2 inches thick or more.
How much extra concrete should I order?
Expect your order to include 5 to 10 percent beyond the amount shown by your dimensions. Because the ground is rarely level, because some concrete always spills, and because the wood frames (forms) holding the wet concrete can bend outward, the amount you use ends up more than your sizes show. If you run short, a second delivery costs much more than having a small amount of concrete left over. Unless you change the setting, the estimator includes an extra 10 percent.
Should I use bags or order ready-mix concrete?
For less than about a cubic yard, bags are the simpler choice. A full yard needs 45 bags at 80 lb. Beyond that amount, truck-delivered ready-mix usually costs less, makes stronger concrete and requires much less work. Ask your concrete company about the smallest order it accepts and any extra fee for a small load.
How much does a yard of concrete cost?
Across the US, ready-mix concrete cost an average of $179.95 per cubic yard during 2025 (Concrete Network, July 2026). The price was usually $160 to $195, without delivery fees. The estimator uses the local price per cubic yard, then shows the material cost.