Work out concrete volume for round, square or rectangular columns. Enter the diameter and height, then see bags, ready-mix pricing and a recommended method.
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A column holds less concrete than its height suggests. The volume comes from the cross-section, and a 14-inch round column takes roughly one-ninth the concrete of a square footing with the same footprint. This concrete column calculator works out the cross-section area, multiplies by height, and returns the volume, weight, bag count, and cost.
Three shapes are covered: round, square, and rectangular. Pick the shape and the diameter field swaps to side length or width-and-depth. Add the height and the number of columns, and the summary updates while you type. The output compares bagged concrete against ready-mix pricing and recommends one based on volume.
It’s for porch columns, carport posts, sonotube piers, and structural columns that need a quick material takeoff before ordering. Enter local prices and the running total tracks them.
Choose your currency from the top dropdown.
Select a column shape: round, square, or rectangular.
Type the diameter, side length, or width-and-depth. The label changes with the shape.
Set the unit for each dimension: in, cm, mm, ft, or m.
Enter the column height, then set its unit.
Adjust how many columns you’re pouring.
Set the waste factor, strength, density, and bag size.
Plug in your price per bag and price per cubic yard.
The Summary tab shows total volume first, then weight, bag count, and both cost paths. Detailed Breakdown lists every value the math passes through, from cross-section area to yield per bag.
Start with the cross-section. That shape decides the area formula. From there, everything else is multiplication.
Formula: Round area = π × (Diameter ÷ 2)²
Formula: Square area = Side × Side
Formula: Rectangular area = Width × Depth
Formula: Volume per column = Area × Height
Formula: Total volume with waste = Volume per column × Count × (1 + Waste %)
Formula: Bags = ⌈ Total volume with waste ÷ (Bag size in lb ÷ 133) ⌉
The 133 constant is pounds of mixed concrete per cubic foot. That’s how an 80 lb bag gets to about 0.60 ft³ of yield. A 60 lb bag yields around 0.45 ft³, and a 40 lb bag yields roughly 0.30 ft³.
Ready-mix runs on volume alone.
Formula: Ready-mix cost = Total volume with waste (yd³) × Price per yd³
If you enter price per cubic meter, the tool multiplies by 0.764555 before the cost runs. The strength dropdown records your PSI target and shows it in the breakdown, but it doesn’t change the bag yield or the volume math.
The recommendation is a single threshold. Above 1 cubic yard, the tool labels ready-mix as recommended. At or below, bags get the nod. That cutoff comes from a simple observation: one cubic yard weighs about 4,000 lbs and takes 45 bags to mix by hand. Past that point, a truck is usually cheaper and always faster.
Worked Example: Four Carport Columns, 14 in Round by 9 ft
Say you’re pouring four round columns for a carport. Each is 14 inches in diameter and 9 ft tall. Waste factor is 10%. Strength is 3,000 PSI. Bag size is 80 lb. Price is $6.50 per bag, and ready-mix is $150 per cubic yard.
Diameter in feet: 14 ÷ 12 = 1.1667 ft
Radius: 0.5833 ft
Cross-section area: π × 0.5833² = 1.0690 ft²
Volume per column: 1.0690 × 9 = 9.621 ft³
Total volume: 9.621 × 4 = 38.48 ft³, or 1.425 yd³
With 10% waste: 42.33 ft³, or 1.568 yd³
Concrete weight: 42.33 × 145 = 6,138 lbs (about 2,784 kg)
Yield per 80 lb bag: 80 ÷ 133 = 0.6015 ft³
Bags needed: 42.33 ÷ 0.6015 = 70.4, rounded to 71
Cost using bags: 71 × $6.50 = $461.50
Cost using ready-mix: 1.568 × $150 = $235.20
Recommended method: Ready-Mix Delivery
The volume crosses the one-yard threshold, so ready-mix wins. At 71 bags, you’d spend roughly twice as much and mix all of it yourself. The savings shrink if the truck can’t reach the pour, in which case a pump fee or wheelbarrow relay eats into the gap.
Volume equals cross-section area times height, times the number of columns. A 12-inch round column, 8 ft tall, takes about 6.28 ft³. Add 10% for waste and you’re at 6.9 ft³, or roughly 12 bags of 80 lb mix.
Square the radius in feet, multiply by pi, then multiply by height. For a 12-inch column that’s 0.5² × 3.1416 × height. Enter the values above and the tool does this for you automatically.
A 12-inch round column, 8 ft tall, needs about 12 bags of 80 lb concrete mix. That’s with 10% waste. At 4 ft tall, the count drops to roughly 6 bags.
A 12-inch Sonotube holds about 0.79 ft³ per foot of height. An 8-inch tube holds about 0.35 ft³ per foot. Multiply by pier height to get the volume for one tube, then by the number of tubes.
Round sheds water better and takes less concrete for the same width. Square is cheaper to form because it uses flat panels. Both work structurally. The choice usually comes down to appearance and forming cost.
Structural columns usually call for 3,500 to 5,000 PSI. Decorative porch columns can run at 2,500 to 3,000 PSI. The strength dropdown in this tool covers 2,500 to 5,000 PSI, but it doesn’t shift the bag count.
Yes, for anything structural. Rebar handles tension that concrete can’t, and ties hold the cage together before the pour. This calculator estimates concrete only. Use a rebar tool for the steel.
Material for a typical 12-inch round column, 8 ft tall, lands under $40 with ready-mix. Bagged concrete runs $60 to $80. Labor and forms add $200 to $500 per column on residential work.
For short columns and small bag counts, yes. A 12-inch round column at 4 ft tall takes about 6 bags, which is manageable by hand. Taller columns or clusters of them get old fast. Past about one cubic yard total, call for a truck.
Check the units first. A diameter entered in inches but read as feet multiplies the volume by about 1,728. Check the count field next. Four columns instead of one will also multiply everything by four.
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