Materials
Concrete Calculator
Cubic yards and cubic feet for slabs, footings, walls and round piers — with a bag count from the yield on your bag, not a guessed constant.
Concrete needed
cubic yards
- Cubic feet
- 48cu ft
- Cubic metres
- 1.36m³
- Bags
- bagsAdd the yield printed on the bag to get a bag count. It differs by product and bag weight.
Ready-mix is sold by the cubic yard. Ask your supplier about the minimum load and the ordering increment before you round.
The working
Area = Length × Width
= 12 ft × 12 ft
= 144 ft²
Volume = Area × Thickness
= 144 ft² × 0.333 ft
= 48 cu ft
Cubic yards = Cubic feet ÷ 27
= 48 ÷ 27
= 1.78 cu yd
1 cubic yard = 3 ft × 3 ft × 3 ft = 27 cubic feet
Enter what you are pouring and its dimensions. The calculator gives the volume in cubic yards, cubic feet and cubic metres, adds the overage you choose, and turns it into whole bags once you enter the yield printed on the bag. It does not pick a thickness for you and it does not price the concrete — those come from your plan and your supplier.
How this calculator works
- Formula version
- 1.1.0
- Last reviewed
- 2026-09-03
- External data
- 1 sources
What this calculates
The volume of concrete a shape needs, in cubic yards because that is how ready-mix is sold, and in cubic feet because that is how bagged mix is labelled. Slabs, footings and walls are rectangular prisms; piers and tubes are cylinders. Everything is exact geometry.
The arithmetic
A slab is length × width × thickness. A footing is the same with its own width and depth, because they are usually in inches while the run is in feet. A wall is length × height × thickness. A round pier is π × diameter² ÷ 4 × height. The result is in cubic feet; dividing by 27 gives cubic yards.
The thickness is entered in inches and converted, so 4 inches is 0.333 feet in the working — the mistake this catches is multiplying feet by inches and getting a number twelve times too big.
Bags
A bag of concrete mix yields a fixed volume once mixed, and that volume is printed on the bag and stated in the manufacturer’s data sheet. It changes with the product and with the bag weight. The calculator divides your cubic feet by that yield and rounds up to whole bags — it never ships a "bags per yard" constant, because there is no such number without knowing which bag.
For one product the data-sheet figures are built in as labelled options: QUIKRETE Concrete Mix No. 1101, whose sheet states 0.30, 0.375, 0.45, 0.60 and 0.675 cubic feet for the 40, 50, 60, 80 and 90 lb bags, and calls each figure approximate. The source is recorded in full below. Any other product: enter the yield from its bag.
Overage
Real subgrades are not flat, forms bow, and some concrete stays in the chute. The overage field adds a percentage you choose to the order quantity. It is blank by default: the right allowance depends on how the subgrade was prepared and how the pour is done, and a default would just be a number pretending to be advice.
What it does not decide
Thickness. A 4-inch patio and a 6-inch driveway are conventions in some places and wrong in others; the load, the soil and the local code decide it. The tool takes what your plan says. It also does not price concrete — ready-mix is quoted per yard with delivery, minimum-load and short-load terms that only your supplier knows.
Worked example
A 12 ft × 12 ft patio, 4 inches thick, with 10% overage
- Length × width
- 12 ft × 12 ft
- Thickness
- 4 in = 0.333 ft
- Overage
- 10%
- Area= 12 × 12= 144 sq ft
- Volume= 144 × 0.333= 48 cu ft
- Cubic yards= 48 ÷ 27= 1.78 cu yd
- Order quantity= 1.78 × 1.10= 1.96 cu yd (52.8 cu ft)
- Bags= 52.8 ÷ yield on the bag= rounded up to whole bags
- Uniform thickness across the pour, and vertical form faces.
- Round piers are true cylinders of the diameter entered.
- Overage and bag yield apply only when entered.
- Bags are rounded up to whole bags.
- It does not model thickened edges, haunches or a slab that changes depth — split those into parts and add them.
- It does not subtract rebar, mesh or embedded items; their volume is normally negligible.
- It does not recommend a thickness, a mix strength or an overage.
- It does not know your supplier’s minimum load or ordering increment.
Common questions
- How many cubic yards is a 10 × 10 slab at 4 inches?
- 100 sq ft × 0.333 ft = 33.3 cu ft, which is 1.23 cubic yards before any overage. Enter 10, 10 and 4 in slab mode and the working shows each step.
- How many bags of concrete make a cubic yard?
- 27 cubic feet divided by the yield printed on the bag. Different products and bag weights yield different amounts, which is why this calculator asks for the figure instead of assuming one. Enter the yield and it gives whole bags for your pour.
- Should I order extra?
- Usually, and the amount depends on the subgrade and the pour. The overage field adds whatever percentage you decide to the order quantity and shows the result separately, so the geometric volume stays visible.
- Does it work in metres?
- Yes. Every dimension accepts metric units and the result is also given in cubic metres. The conversions are exact.
Where people go next
All materials tools →Ordered by what usually comes next in the same job, not by keyword.