How do you calculate the volume of a concrete cylinder?+
For a solid cylinder, use pi times radius squared times height, then divide cubic feet by 27 to convert to cubic yards. A 12 inch diameter cylinder at 4 feet tall contains about 0.116 cubic yards. Hollow cylinders use the same concept, except you subtract the inner void from the outer cylinder first. The calculator above handles both solid and hollow geometry so you do not need to work through the conversions manually each time.
What is the difference between the cylinder calculator and the column calculator?+
The column calculator is best when you need both round and square column takeoffs in one place. The cylinder calculator focuses entirely on circular geometry and adds hollow-cylinder capability, which makes it a better fit for ring foundations, tank walls, caisson liners, and any annular shell where a center void remains. If you only need a standard round post or pier, either tool can work, but the cylinder page gives more depth on circular applications.
How much concrete do I need for a tube form?+
Tube form quantity depends on form diameter and pour depth. A 6 inch tube at 2 feet deep contains about 0.029 cubic yards, which is a little over one 80 lb bag after you include overage. A 10 inch tube at 3 feet deep is roughly 0.091 cubic yards, and a 12 inch tube at 4 feet deep is around 0.116 cubic yards before waste. Multiply the single-form volume by quantity and then add 10% before ordering.
How do I calculate a hollow cylinder volume?+
First calculate the inside diameter by subtracting twice the wall thickness from the outer diameter. Then use pi times height times the difference between the outer radius squared and inner radius squared. For example, a 48 inch outside diameter cylinder with a 6 inch wall has a 36 inch inner diameter. At 4 feet tall, that shell contains about 0.814 cubic yards before overage and about 0.895 cubic yards with a 10% order allowance.
How deep should a concrete cylinder pier be?+
Pier depth depends on frost depth, soil bearing conditions, and the load carried by the pier. In mild climates, light residential piers may only need 12 to 18 inches of embedment, while colder regions often require piers to extend below the local frost line, which can be 48 inches or more. Large caissons for structural loads may run 10 to 30 feet or deeper depending on soil conditions and engineering requirements.
How many bags of concrete do I need for a round column?+
Take the total order volume, including 10% overage, and divide by the yield per bag. For 80 lb bags, one bag yields about 0.022 cubic yards. A 12 inch diameter column at 8 feet tall contains about 0.232 cubic yards, or about 0.255 cubic yards with overage, which works out to roughly 12 bags of 80 lb mix. Once you scale that up across several identical columns, ready-mix usually becomes more efficient than hand-mixing bags.
What size tube form do I need?+
Choose a tube form diameter that matches the finished outside diameter required by the design. Common residential sizes are 6 to 8 inches for fence and mailbox posts, 10 to 12 inches for deck piers, and 12 to 18 inches for larger columns or flagpole bases. Cut the form to the required height, brace it plumb, and use the same diameter in the calculator so the volume output aligns with the material you actually buy.
Can I use the cylinder calculator for a concrete test cylinder?+
Yes, the geometry is the same, so the math works for standard test cylinders. A common 4 inch by 8 inch test cylinder contains less than 0.001 cubic yards of concrete, which is only a small fraction of a bag. In practice, test cylinders are filled from the same batch as the main structural pour, so they do not usually drive ordering. The calculator is much more useful for piers, columns, caissons, tank walls, and other field pours.