Concrete Calculator
Concrete volume for slabs, footings, walls and round columns, in cubic yards and cubic metres. Thickness has its own inches box, because that is where concrete estimates usually go wrong.
Switching units keeps your measurements. Nothing is reset.
What are you pouring?
A 4 in slab is 0 ft 4 in, not 4 ft.
Waste allowance
10% covers uneven subgrade, spillage and the little extra you always want at the far end of a pour.
Offcuts, breakages, pattern matching and the occasional damaged piece all mean you use more material than the bare area. Keeping a few spare pieces for future repairs is also normal.
This is a planning allowance, not a rule. Adjust it for your layout, your material and your own tolerance for a second trip to the store.
Estimated cost
Cost uses the price you enter. This product never shows invented market prices.
Your result appears here
Enter your measurements to see how much material to buy.
How to use this calculator
- 1
Choose what you are pouring. Slab, footing and wall are all rectangular; the labels change so you are asked for a thickness where a thickness is what you measure.
- 2
Enter the thickness in the inches box. A 4 in slab is 0 ft 4 in. Putting 4 in the feet box would order twelve times too much.
- 3
Add a pour for each separate element. A slab with a thickened edge, or four post footings, are separate pours added together.
- 4
Read cubic yards if you are ordering ready-mix, or switch to bags with the concrete bag calculator if you are mixing it yourself.
A worked example
A 10 ft × 10 ft slab at 4 in thick, plus a 10 ft × 1 ft thickened edge 12 in deep, with a 10% overage:
Add the sections together
33.33 ft³ + 10 ft³43.33 ft³
Add the overage
43.33 ft³ × 1.147.67 ft³
Convert to the unit you order in
47.67 ft³1.77 yd³
You will need
1.77 yd³
This example is produced by running the calculator above, so it always matches what the tool does.
The formula
A slab, footing or wall is length × width × thickness. A round column is π × radius² × height, where the radius is half the diameter. Sections are converted to a common unit before being added, so mixing feet, inches and metres is safe. The overage is applied to the total, and one cubic yard is exactly 27 cubic feet.
Ordering concrete
Running short is much worse than running over
A pour that stops halfway leaves a cold joint you cannot undo. The overage exists for that reason, and most people order a little more than the geometry alone suggests.
Subgrade is never as flat as the drawing
A slab specified at four inches will average more than four inches over real ground. If the base is rough, an overage at the higher end of the range is realistic rather than cautious.
This is a quantity, not a design
Thickness, reinforcement, mix strength and base preparation are structural decisions. This calculator tells you how much concrete fills the shape you described; it does not tell you whether that shape is right for the load.
Common questions
- How many cubic yards of concrete do I need for a 10x10 slab?
- At four inches thick, a 10 ft × 10 ft slab is 100 square feet × 0.333 feet, which is 33.3 cubic feet, or 1.23 cubic yards before any overage.
- How many cubic feet are in a cubic yard of concrete?
- Exactly 27, the same as any other material. Ready-mix is ordered by the cubic yard in the US and by the cubic metre elsewhere.
- Should I order extra?
- Most people do. The overage above is adjustable, and how much you add depends on how even your base is and how much a second delivery would cost you.