Concrete Column Calculator
Calculate the concrete needed for round columns, sonotubes, and square or rectangular columns and posts. Get cubic yards, cubic feet, cubic meters, per-column volume, pre-mix bag counts, ready-mix truck loads, and a downloadable PDF estimate.
Volumes are geometric estimates. Add waste for spillage, form bulge, and over-dig at the base, and order a little extra rather than running short. For planning purposes only.
| Bag Size | Yield | Bags Needed | Total Weight | Est. Cost |
|---|
Bag counts cover the full — ft³ (waste included). Bag cost uses your bag price scaled per size.
How to use the concrete column calculator
Four quick steps turn your column dimensions into cubic yards, bag counts, truck loads, and a cost comparison — whether you’re pouring sonotubes, deck posts, or square piers.
Pick your column shape
Round/tube or square/rectangular. Each shape asks only for what it needs — or tap a preset like Sonotube 16″ or 4 Deck Posts.
Enter dimensions
Diameter or width × depth in inches, height in feet, and how many columns. The tool handles the unit conversions.
Set waste, bag & prices
Add a 5–10% waste allowance for form bulge, pick a bag size, and enter ready-mix and bag prices for costing.
Read results & save a PDF
Get yards, feet, meters, per-column volume, bag counts, truck loads, and a bag-vs-ready-mix cost — then download a PDF.
How column volume is calculated
A column is just an area extruded up its height. Round columns use the area of a circle; square columns use width × depth. Here is the exact formula behind each shape, both producing cubic feet.
Worked example — four 12″ round columns, 9 ft tall
Radius: (12/12) ÷ 2 = 0.5 ft
Per column: π × 0.5² × 9 = 7.07 cu ft
All four: 7.07 × 4 = 28.3 cu ft = 1.05 cu yd
80 lb bags (with 10% waste): 31.1 ÷ 0.60 = 52 bags
With 10% waste → order about 1.15 cu yd, or ~52 80-lb bags.
Column estimating charts
Handy lookups for the most common column questions — sonotube volumes, square-column volumes, and typical jobs. Figures exclude waste, so add 5–10% to your final order.
| Diameter | Cu ft per ft | 9 ft column (cu ft) | 9 ft column (80 lb bags) |
|---|---|---|---|
| 8 in | 0.35 ft³ | 3.14 ft³ | 6 bags |
| 10 in | 0.55 ft³ | 4.91 ft³ | 9 bags |
| 12 in | 0.79 ft³ | 7.07 ft³ | 12 bags |
| 16 in | 1.40 ft³ | 12.57 ft³ | 21 bags |
| 18 in | 1.77 ft³ | 15.90 ft³ | 27 bags |
| 24 in | 3.14 ft³ | 28.27 ft³ | 48 bags |
Multiply “cu ft per ft” by your column height and count. Bag counts are rounded up and exclude waste.
| Size | Cu ft per ft | 9 ft column (cu ft) | 9 ft column (80 lb bags) |
|---|---|---|---|
| 8 × 8 in | 0.44 ft³ | 4.00 ft³ | 7 bags |
| 10 × 10 in | 0.69 ft³ | 6.25 ft³ | 11 bags |
| 12 × 12 in | 1.00 ft³ | 9.00 ft³ | 15 bags |
| 12 × 16 in | 1.33 ft³ | 12.00 ft³ | 20 bags |
| 16 × 16 in | 1.78 ft³ | 16.00 ft³ | 27 bags |
Cu ft per ft = (width/12) × (depth/12). A square column of the same width holds more than a round one, since the circle fits inside the square.
| Job | Dimensions | Cubic feet | Cubic yards | 80 lb bags |
|---|---|---|---|---|
| 4 deck posts | 8″ dia × 4 ft | 5.6 ft³ | 0.21 yd³ | 10 bags |
| Single sonotube | 16″ dia × 4 ft | 5.6 ft³ | 0.21 yd³ | 10 bags |
| 6 posts | 10″ dia × 9 ft | 29.5 ft³ | 1.09 yd³ | 50 bags |
| 2 square piers | 10×10″ × 8 ft | 11.1 ft³ | 0.41 yd³ | 19 bags |
| 4 square columns | 12×12″ × 9 ft | 36.0 ft³ | 1.33 yd³ | 60 bags |
Under ~1 cubic yard, bagged mix usually beats ready-mix once short-load fees are added. Bag counts exclude waste.
| Bag size | Yield | Bags per cu yd | Best for |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 90 bags | Small posts, easy lifting |
| 50 lb | 0.375 ft³ | 72 bags | Light posts & tubes |
| 60 lb | 0.45 ft³ | 60 bags | Piers & medium tubes |
| 80 lb | 0.60 ft³ | 45 bags | Best value per ft³ |
Bag counts are always rounded up. Yields are typical for standard pre-mix — check your product’s stated yield.
Everything the calculator works out
One set of column dimensions gives you every number needed to order confidently — whether you’re mixing bags or booking a truck.
Key figures every column depends on
Built for any column pour
From a handful of deck posts to a row of structural piers, the same calculator scales to the job.
Setting deck posts, mailbox posts, or pergola footings in sonotubes and wants the exact bag count per tube.
- Start from a preset like 4 Deck Posts
- Use the sonotube table by diameter
- Let it flag when bags beat ready-mix
Pouring porch columns, carport piers, or basement supports and needs cubic yards fast.
- Batch identical columns by quantity
- Compare round vs square volume
- Keep the PDF on file for quotes
Scoping a build with tubes, posts, and piers all rolled into one materials budget.
- Model each column size separately
- Total the yards for pour-day trucks
- Use cubic meters for metric specs
7 tips for an accurate column pour
Small habits keep your order right the first time and your columns straight, strong, and void-free.
Concrete column calculator FAQ
The formulas, tube volumes, and ordering questions people ask most before pouring columns.
It depends on the shape, worked in matching units:
• Round / sonotube: π × (dia/2, in ft)² × H(ft) × qty
• Square / rectangular: W(ft) × D(ft) × H(ft) × qty
Convert inches to feet (÷12), then divide total cubic feet by 27 for cubic yards. Example: four 12″ round columns 9 ft tall = 4 × π × 0.25 × 9 = 28.3 cu ft = 1.05 cu yd. Add 5–10% for waste.
Concrete per foot of height, by tube diameter:
• 8 in: ~0.35 cu ft/ft • 10 in: ~0.55 cu ft/ft
• 12 in: ~0.79 cu ft/ft • 16 in: ~1.40 cu ft/ft
• 18 in: ~1.77 cu ft/ft • 24 in: ~3.14 cu ft/ft
Multiply by height and the number of tubes. Example: a 12″ sonotube 9 ft tall = 0.79 × 9 = 7.1 cu ft, or about twelve 80-lb bags.
Use Volume = π × radius² × height, with the radius in feet.
Convert the diameter from inches to feet (divide by 12), then halve it for the radius. Example: a 16″ tube gives a radius of (16/12) ÷ 2 = 0.667 ft; the area is π × 0.667² = 1.40 sq ft; multiply by the height and the number of columns. Divide the total by 27 for cubic yards.
Use Volume = Width × Depth × Height, all in feet.
Convert inch dimensions to feet by dividing by 12. Example: a 12 × 12″ column 9 ft tall = 1 × 1 × 9 = 9 cu ft = 0.33 cu yd, or about fifteen 80-lb bags. Multiply by the number of columns and add 5–10% for waste.
Divide the total cubic feet by the bag yield and round up:
• 80 lb bag: ~0.60 cu ft (45 bags per cu yd)
• 60 lb bag: ~0.45 cu ft (60 bags per cu yd)
• 40 lb bag: ~0.30 cu ft (90 bags per cu yd)
A 12″ tube 9 ft tall (7.1 cu ft) needs about twelve 80-lb bags. Bags are practical under roughly 1 cubic yard; above that, ready-mix is cheaper and far less labor.
Deck posts set in sonotubes use the round-column formula, usually with 8 to 10 inch tubes. Four 8″ tubes at 4 ft deep = 4 × 1.40 = 5.6 cu ft, or about ten 80-lb bags.
Post depth must reach below your local frost line and the tube diameter is a structural choice, so confirm both with your building department or a deck-footing chart before ordering.
Under about 1 cubic yard, bagged mix usually wins once ready-mix short-load fees are added — good for a few deck posts or tubes. One cubic yard is roughly 45 80-lb bags.
Above about 1 cubic yard — several tall columns or large piers — ready-mix is faster, cheaper, and gives a continuous pour. A concrete pump or chute helps when tubes are tall or hard to reach.
Add a 5 to 10 percent waste allowance for spillage, form bulge, and over-dig at the base of the tube. Cardboard tubes can belly out slightly under the pressure of wet concrete, and the hole beneath often takes more than planned.
Round up to full bags or to the next quarter cubic yard for ready-mix. Running short mid-pour risks a weak cold joint in the column.
General Estimating Notice: This calculator provides geometric volume and bag-count estimates based on user input and standard material yields. Actual quantities vary with form bulge, base over-dig, and spillage, so order a little extra rather than running short. Column diameter, size, reinforcement, and footing depth are structural decisions — verify them with your local building code and engineer before ordering. For planning purposes only.