Concrete columns
This sonotube calculator, also your concrete column calculator, turns a tube diameter, height, and tube count into the number of 80 lb bags and the total cost for all round concrete posts. Tube sizes offered are 8, 10, and 12 inches in diameter.
Columns
Tap or type into any yellow number on the drawing to change it.
Avg US retail price, checked Aug 2026.
Start with the tube diameter and halve it to get the radius. Multiply the radius by itself, then by the height of the tube, then by pi. That gives the volume of one tube. Multiply that by the number of tubes you are pouring to get the total column volume. Add 10% for waste. That allowance accounts for spillage and for concrete that rises above the rim of the tube. You cast a cylindrical post or pier by pouring concrete into a sonotube, a round cardboard tube. The 80 lb bag yields 0.6 cu ft. The average price per bag is $5.98, checked Aug 2026.
Depending on which unit system you choose, the height field shows feet or inches, or meters or centimeters.
What tube diameters does this calculator support?
The calculator works with 8, 10, and 12 inch diameter tubes. Choose the one that matches the round form you are pouring.
When you enter the number of tubes, how does the bag total change?
The calculator first finds the volume of a single tube at the height you entered, then multiplies it by the number of tubes. A 10% waste factor is added on top, so the bag count and cost cover all of the posts together.
What is a sonotube used for?
You pour concrete into a round cardboard tube, called a sonotube, to cast a cylindrical post or pier. Deck posts, fence posts, and pergola footings are common uses.