Concrete Estimator
Enter the size of your job to get cubic yards, cubic meters and bags needed.
How to use the concrete estimator
- Choose a shape: a slab, a footing, a wall, a 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 12 ft 6 in, enter 12'6" (the ' means feet and the " means inches). For 3½ in, enter 3 1/2.
- Check the cubic yards and bags. Your chosen extra for spills and uneven ground is already counted, so buy that amount.
How the concrete estimator works
You can buy concrete in bags that you mix yourself, or as ready-mix, which means concrete mixed at a plant and delivered by truck. One cubic yard fills a cube measuring 3 feet along each side (27 cubic feet). Ready-mix is sold by the cubic yard. The tool changes your sizes into cubic feet, then adds the amount you picked for spills and uneven ground, and gives the answer as cubic meters (the metric unit), cubic yards and whole bags.
Concrete volume formula
Put in your sizes, and the tool tells you how much to buy. With 10% extra for spills and uneven ground, a 10 ft by 10 ft patio, 4 in thick, takes 1.36 cubic yards instead of 1.23.
See the formula
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. The number 12 converts inches to feet, and 27 converts cubic feet to cubic yards, since 27 cubic feet fit inside a cubic yard. With a round column, the tool works out the circle's area using the width measured straight across.
How many bags of concrete per cubic yard
The larger a bag is, the more concrete it makes, so fewer bags are needed. A cubic yard needs 45 big 80 lb bags, or 90 small 40 lb ones. The figures come from two big US brands of bagged concrete, Quikrete and Sakrete, and every size appears in the table. If you need only part of a bag, the tool counts a whole bag, so you never run 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?
Cubic feet come from multiplying length, width and thickness, all in feet. Divide by 27 for cubic yards. At 10 by 10 feet and 4 inches thick, a slab holds 33.3 cubic feet, which is 1.23 cubic yards. Before you order, add 5 to 10 percent more for spills and uneven ground.
How much concrete do I need for a 10x10 slab?
A slab that measures 10 feet by 10 feet and is 4 inches thick needs 1.23 cubic yards of concrete. With 10 percent more for spills and uneven ground, the total is about 1.36 cubic yards. That comes to about 62 bags in the big 80 lb size. Smaller bags mean more of them: 82 bags of 60 lb, then 98 of 50 lb, and 123 of 40 lb. Make it 6 inches thick and it 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 makes about 0.60 cubic feet (the number Quikrete and Sakrete both list). That means 45 bags fill a cubic yard, and a cubic yard is 27 cubic feet.
How many cubic feet are in a 60 lb or 50 lb bag of concrete?
About 0.45 cubic feet comes from a 60 lb bag, and about 0.375 cubic feet from a 50 lb bag. So a cubic yard needs 60 bags at 60 lb, or 72 bags at 50 lb. One 40 lb bag gives 0.30 cubic feet, and a yard needs 90 of them.
How thick should a concrete slab be?
The thickness you'll usually use for a patio, a walkway or a shed floor is 4 inches. Driveways and garage floors that take cars and trucks need a thickness of 5 to 6 inches. Bagged mix works for slabs that are 2 inches thick or more.
How much extra concrete should I order?
Plan on ordering 5 to 10 percent beyond what your sizes show. Some concrete always spills, the ground is rarely level, and the wood frames (forms) holding the wet concrete can bend outward, so you end up using more than your sizes say. If you run short and pay for a second delivery, that costs far more than having a little concrete left over. Unless you change it, the estimator adds 10 percent.
Should I use bags or order ready-mix concrete?
For less than a cubic yard or so, bags are the easier pick; one full yard needs 45 bags at 80 lb. Beyond that, ready-mix from a truck usually costs less, gives stronger concrete and takes far less work. Ask your concrete company for the smallest order it takes, and if a small load costs extra.
How much does a yard of concrete cost?
During 2025, the average price for ready-mix concrete in the US was $179.95 for each cubic yard (Concrete Network, July 2026). The typical range was $160 to $195, without delivery fees. Type your local price for each cubic yard into the estimator and it shows the material cost.