Sonotube Concrete Calculator Guide: How Much Concrete for a Column

A Sonotube — the fiberboard cylinder that forms round concrete columns, piers, and deck supports — seems like an easy pour until you try to estimate the concrete. Because the tube is a cylinder rather than a slab, the volume math is different, and getting it wrong is expensive in both directions. This guide walks through the cylinder formula, gives exact bag counts for common tube sizes, and covers the mistakes that burn concrete on every column pour.

The Cylinder Volume Formula

Concrete volume in a Sonotube is calculated with the formula for the volume of a cylinder:

Volume (ft3) = pi x Radius2 x Height

Radius is half the tube's inside diameter, and everything must be in the same unit. Take a common 12-inch Sonotube that is 3 feet tall. The radius is 6 inches, or 0.5 feet. So the volume is 3.1416 x 0.5 x 0.5 x 3 = 2.36 cubic feet. That works out to just under 4 bags of 80 lb mix (2.36 / 0.60 = 3.9 bags), or about 4.4 bags with a 10% waste factor. For a taller 12-inch tube at 6 feet, the volume doubles to 4.71 cubic feet, needing about 8 bags of 80 lb mix — 9 with waste.

Bag Counts by Tube Size

Here is the finished volume and bag count for the most common Sonotube diameters, per foot of height. These assume a straight, level tube and a clean pour:

• 8-inch tube: 0.35 ft3 per foot, about 0.6 bags of 80 lb per foot
• 10-inch tube: 0.55 ft3 per foot, about 1 bag of 80 lb per foot
• 12-inch tube: 0.79 ft3 per foot, about 1.3 bags of 80 lb per foot
• 16-inch tube: 1.40 ft3 per foot, about 2.3 bags of 80 lb per foot
• 18-inch tube: 1.77 ft3 per foot, about 3 bags of 80 lb per foot

To get your total, multiply the per-foot figure by the tube height in feet, then multiply the bag count by 1.10 for waste. For example, a 16-inch tube at 5 feet needs 1.40 x 5 = 7 cubic feet, or 7 / 0.60 = 11.7 bags of 80 lb, which rounds to 13 bags with waste. If you are ordering a truck instead, divide the total cubic feet by 27 to get yards — 7 cubic feet is only 0.26 yards, far below the typical truck minimum, so a single Sonotube is almost always a bag job.

Why Columns Waste More Than You Think

Sonotube pours are notorious for underestimation because three things go wrong. First, the tube is rarely perfectly vertical — even a few degrees of lean means the effective height is greater than the measured side, and the base bell-out eats volume. Second, tubes settle and shift during the pour, so the concrete column is often bigger than the nominal diameter. Third, the fiberboard tube wicks water out of the mix and can expand slightly, adding volume you did not plan for. For all of these reasons, the 10% waste factor is not optional on a Sonotube pour — and if you are setting the tube in an excavated bell (a wider base to spread the load), add the bell's volume as a separate calculation.

Ordering the Concrete

Because a single Sonotube is almost always under the ready-mix minimum, most homeowners mix bags. Budget for the bag count above, then buy one or two extra bags so a shortfall never forces a cold joint in the middle of a column — a repair that requires digging out and re-pouring the entire pier. If you have many tubes or a deep footing, price a truck: a group of columns totaling more than about half a yard can make the short-load fee worthwhile. When you pour, use a concrete chute or a piece of gutter to direct the mix to the bottom of the tube and vibrate or rod the concrete as you fill to remove air pockets — a void near the bottom is a structural weak point you cannot see until the column cracks under load.

To calculate any Sonotube, enter the diameter and height into the concrete calculator at the top of this page and choose the cylinder shape. It returns the cubic yards, the bag counts for 40, 60, and 80 lb sizes, and the truck comparison automatically.