Concrete Calculator

Concrete is ordered by the cubic yard, which is 27 cubic feet. The tool multiplies your length, width, and thickness to get cubic feet, then divides by 27. As a feel for scale, a 10 by 10 slab at 4 inches thick is about 1.2 cubic yards, and most ready-mix trucks carry around 10 yards.

Bags make sense for small pours like a few post footings or a tiny pad — but it takes roughly 40 to 60 bags to make a single cubic yard, so the math turns against you fast. Once you are past about half a yard, a ready-mix delivery is usually cheaper and far less work. The tool shows both so you can decide.

Order about 10% over your calculated volume. Subgrades are never perfectly level, forms bulge, and you always lose a little to spillage and what sticks in the chute. Running short on a pour is a real problem because a cold joint forms while you wait for more, so it is far better to have a little extra.

Four inches is standard for patios, sidewalks, and shed pads. Bump to five or six inches for a driveway or anywhere a vehicle parks, and thicker still for heavy loads. Remember to enter slab thickness in inches here — the tool converts it for you, but using feet by mistake throws the volume off by a factor of twelve.

Use the round column option and enter the tube diameter in inches and the height in feet. The tool uses the area of a circle times the height, so a 12-inch Sonotube pier 8 feet tall comes out to about 6.3 cubic feet, or roughly a quarter yard. Add a few percent waste since cardboard tubes can bow when filled.

Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.

Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.

Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.