Concrete Column Calculator

1. Choose the column shape: round for a cylinder or sonotube form, square for a square column.
2. Enter the diameter or side in inches and the height in feet.
3. Set the number of columns for identical piers or posts, and a 5 to 10 percent waste allowance.
4. Pick a bag size if you want a bag count, then read the cubic yards to order.

Here is what each result line means:

A concrete column calculator turns the size and height of a vertical concrete element into the amount of concrete to order. It covers round columns, piers and sonotube forms, and square or rectangular columns, measured on one side.

Columns and piers carry load down to a footing, so they are usually poured together with foundation work. Concrete is sold by the cubic yard for ready-mix or by the bag for small pours, so the tool converts inches and feet into both and adds a waste allowance. To get the mix proportions right use the concrete mix calculator, and for the binder in the mix use the cement calculator.

A round column is a cylinder, so its volume is the area of the circle times the height, where the circle area is pi times the radius squared. A square column is a prism, so its volume is the side squared times the height.

1. Convert the diameter or side from inches to feet by dividing by 12.
2. For a round column, halve the diameter for the radius, then find pi times the radius squared for the area; for a square column, square the side.
3. Multiply the area by the height for one column, then by the number of columns, and add the waste allowance.
4. Divide by 27 for cubic yards and by the bag yield for a bag count.

Mixing water for the pour is a separate question; size it with the water cement ratio calculator.

Suppose you are pouring 4 round deck piers in 12 inch sonotube forms, each 9 feet tall, with 10 percent waste.

Calculation: the diameter is 12 / 12 = 1 ft, so the radius is 0.5 ft. The area is pi x 0.5 x 0.5 = 0.785 sq ft. One pier is 0.785 x 9 = 7.07 cu ft, and four are 28.3 cu ft. Adding 10 percent waste gives 31.1 cu ft, or 1.15 cu yd, about 52 eighty-pound bags.

The lesson: four tall piers add up fast, so at over a cubic yard a short-load delivery usually beats mixing 52 bags by hand.

The shape changes the area formula, and a round column of the same nominal size holds less concrete than a square one because the circle fits inside the square.

For the delivered price of either pour, the concrete cost calculator in the related tools prices it by the yard.

Diameter or Side

The size enters the area as a square, so it moves the volume more than anything else. Doubling the diameter roughly quadruples the concrete per foot of height.

Height

Height multiplies the area directly, so a tall pier uses proportionally more concrete. Measure from the top of the footing to the top of the pour.

Number of Columns

Pier and post jobs multiply one column by the count, so a small error per column is multiplied across the job. Confirm the single-column volume first.

Over-fill and Spillage

Tubes are usually over-filled slightly at the top and lose concrete to the barrow and the pour. A 5 to 10 percent allowance covers it.

Cardboard tube forms are sold by inside diameter, which is the diameter you enter here. A taller tube simply multiplies the per-foot volume, so you can read the volume per column to see how much one tube takes.

These are rounded guides from the same pi times radius squared formula the tool uses; enter your exact diameter and height above for the real figure.

Ordering Concrete for Piers and Posts

Size the order in cubic yards and add waste before you call the supplier, so you can pour all the columns in one visit.

Buying Sonotube and Bags

The volume per column tells you how much concrete one tube takes, so you can buy the right number of bags for a small job.

Planning a Deck or Fence

Deck piers and heavy fence posts are repeated columns; the quantity field totals them so you order once for the whole run.

1. Using Radius Instead of Diameter

The field asks for the diameter; the tool halves it for the radius. Entering the radius as the diameter quarters the result. Measure the full width of the tube or side.

2. Mixing Up Inches and Feet

Enter the diameter or side in inches and the height in feet, as the fields are labelled. Swapping them throws the volume off badly.

3. Forgetting the Quantity

Entering one pier but leaving the count at 1 under-orders a whole deck. Set the number of columns for identical piers and posts.

4. Ignoring the Footing

The bell or pad at the base of a pier is extra concrete beyond the column. Work the footing out separately and add it.

5. Treating the Estimate as a Structural Spec

Volume is not strength. Column size, reinforcement and load capacity come from a code or an engineer, not from this tool.

The arithmetic is exact; the usefulness depends on the size, height and quantity you enter.

Halve the diameter for the radius, find pi times the radius squared for the area in square feet, then multiply by the height in feet. A 12 inch round column is pi x 0.5 x 0.5 = 0.785 square feet, so a 9 foot pier is about 7.07 cubic feet before waste.

It depends on the diameter and height. An 8 inch tube holds about 0.35 cubic feet per foot of height, a 10 inch about 0.55, and a 12 inch about 0.79. Enter your tube diameter and height above and read the volume per column for the exact figure.

Convert the side to feet, square it for the area, then multiply by the height. A 10 inch square column is 0.833 x 0.833 = 0.69 square feet, so an 8 foot column is about 5.55 cubic feet before waste.

A square column uses more than a round one of the same nominal size, because the circle fits inside the square and fills about 79 percent of it. Pick the shape that matches your form; the tool applies the right area formula.

It depends on the size and height. Four 12 inch round piers 9 feet tall take about 52 eighty-pound bags with waste. The tool gives the bag count for your columns and bag size, rounded up, so you can see if mixing by hand is realistic.

Enter the height of the concrete pour in feet, usually from the top of the footing to the top of the column or tube. Do not include the footing itself; size that separately with a footing calculator.

Yes, a 5 to 10 percent allowance. Tubes are over-filled slightly at the top, and concrete is lost to the barrow and the pour, so a margin stops you running short across several columns.

No. It estimates the concrete volume once you enter the size and height. The required column size, reinforcement and load capacity come from your plans, local code or a structural engineer.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• QUIKRETE Concrete Mix 1101 data sheet (QUIKRETE; bag yields 0.60, 0.45 and 0.30 cu ft).
• National Ready Mixed Concrete Association (NRMCA; ready-mixed concrete and ordering).
• American Cement Association (American Cement Association; concrete basics).