Concrete Tube Calculator

Sonotube and similar cardboard concrete forming tubes are the standard method for pouring cylindrical footings and piers. Deck posts, fence posts, pergola supports, mailbox posts, and pier foundations all use this approach. The tube acts as both the form and a barrier between the concrete and surrounding soil. This calculator handles the volume for any number of identical tubes. Enter the tube diameter in inches (common sizes are 8, 10, 12, 14, 16, and 24 inches), the depth you are filling in feet, and how many tubes you are pouring. The result is the total cubic yards of concrete needed for all tubes combined. For deck footings, most building codes require the bottom of the footing to extend below the local frost line. In northern states this can be 36 to 48 inches deep. In southern states it may only be 12 to 18 inches. Check your local building code or call your building department before digging. A footing that does not reach below the frost line will heave and shift as the ground freezes and thaws. Common tube diameter recommendations depend on the load. An 8-inch tube works for light-duty fence posts. A 10 to 12-inch tube is standard for most deck footings. Larger structures like pergolas or elevated decks may require 14 to 16-inch tubes. Your building plans or engineer should specify the required diameter. To set the tubes, dig the hole about 2 inches wider than the tube diameter, level the bottom with a few inches of gravel for drainage, drop the tube in, and brace it plumb. Pour the concrete in 12-inch lifts, poking a piece of rebar in and out of each lift to remove air pockets. Set your post bracket or anchor bolt in the top before the concrete sets up.