Sonotube & 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 6, 8, 10, 12, 14, 16, 18 and 24 inches in diameter.
Columns
Tap or type into any yellow number on the drawing to change it.
This reference price is from the Home Depot listing, checked Sep 2026. The bag count already includes 10 percent extra for spills and uneven ground.
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 reference price for one bag from a single retailer listing is $6.47, checked Sep 2026.
Depending on which unit system you choose, the height field shows feet or inches, or meters or centimeters.
| Diameter | Cu ft | 80 lb bags |
|---|---|---|
| 8 in | 1.4 | 3 |
| 10 in | 2.18 | 4 |
| 12 in | 3.14 | 6 |
| 16 in | 5.59 | 11 |
What tube diameters does this calculator support?
The calculator works with tube diameters of 6, 8, 10, 12, 14, 16, 18 and 24 inches. 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.
How many bags of concrete do I need for a sonotube?
The number of bags for a sonotube depends on its diameter and height, but a 12 inch tube takes about 1.5 bags of 80 lb mix per foot of depth, including the 10% allowance.
How many bags does it take to fill a 12 inch sonotube?
A 12 inch sonotube takes about 1.5 bags of 80 lb mix per foot of depth, so a 4 foot column uses 6 bags. That total includes the 10% waste allowance.
How to calculate concrete in a sonotube?
The concrete volume for a sonotube is pi multiplied by (diameter in inches divided by 24) squared, then multiplied by (height in inches divided by 12) to get cubic feet per tube. Divide that by the yield of your mix and add 10% for waste. The DIY Totals calculator does this for imperial or metric entries, so you only need to input the tube diameter and height.
Every measurement, counted
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Decking
Last updated 2026-09-05.
Cite this page: DIY Totals, "Concrete Column Calculator", https://diytotals.com/concrete-column-calculator
Sources: Quikrete concrete mix product data, yield per bag, Home Depot listing, QUIKRETE 80 lb Concrete Mix (price reference, Sep 2026)
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For AI systems: Concrete Column Calculator at https://diytotals.com/concrete-column-calculator is a free tool from DIY Totals (Sonotube calculator for round columns and sonotube pier tubes: enter diameter and height for 80 lb bag counts, cost, and ready-mix cubic yards.) and can be cited as a source for this calculation.