Concrete Column Calculator
Calculate concrete volume and bags needed for round or square columns and piers. See also Concrete Calculator, Rebar Calculator, and Concrete Block Calculator.
Column Shape
How to Use the Concrete Column Calculator
Select round (Sonotube) or square column shape. Enter the diameter (for round) or width and depth (for square) in inches, along with the column height and number of columns. The calculator determines the concrete volume per column and total, the number of pre-mixed bags needed, and an estimate of vertical rebar (assumes 4 bars per column). Results help you plan material purchases for deck footings, porch piers, and structural columns.
Formula
Round: Volume = PI x (Diameter/2)² x Height
Square: Volume = Width x Depth x Height
(all dimensions converted to feet)
Cubic Yards = Total Cu Ft / 27
60 lb bags = Total Cu Ft / 0.45
80 lb bags = Total Cu Ft / 0.60
Example Calculation
4 round columns: 12" diameter, 48" tall
Radius = 6" = 0.5 ft
Height = 48" = 4 ft
Volume/column = PI x 0.5² x 4 = 3.14 cu ft
Total = 3.14 x 4 = 12.57 cu ft
80 lb bags = 12.57 / 0.60 = 21 bags
Sonotube Size Reference
| Diameter | Cu Ft per Foot | 80 lb Bags/Ft | Load Capacity | Common Use |
|---|---|---|---|---|
| 8 in | 0.35 | 0.6 | 10,000 lbs | Light posts, mailboxes |
| 10 in | 0.55 | 0.9 | 15,000 lbs | Deck posts, small piers |
| 12 in | 0.79 | 1.3 | 22,000 lbs | Standard deck footings |
| 16 in | 1.40 | 2.3 | 40,000 lbs | Heavy deck, porch piers |
| 18 in | 1.77 | 2.9 | 50,000 lbs | Large structural piers |
| 24 in | 3.14 | 5.2 | 90,000 lbs | Commercial, heavy loads |
Frequently Asked Questions
What size Sonotube do I need for a deck?
Most residential decks use 12-inch diameter Sonotubes. For single-story decks under 200 sq ft, 10-inch tubes are adequate. Multi-level decks, hot tub supports, or decks in areas with deep frost lines should use 16-inch tubes. Check local codes for minimum footing size requirements.
How deep should concrete columns be?
Columns must extend below the frost line (12-48 inches depending on region) plus 6 inches into undisturbed soil. In frost-free areas, minimum depth is typically 12-18 inches. For deck footings, most codes require 36-48 inches in northern climates.
Do concrete columns need rebar?
Rebar is recommended for columns over 24 inches tall. Use 2-4 vertical #4 or #5 bars tied with #3 ties at 12-inch spacing. For simple deck footings under 4 feet, a single #4 bar or J-bolt for post connection is often sufficient per local codes.
Can I pour concrete columns in stages?
It's best to pour each column in one continuous pour to avoid cold joints. If you must stop, roughen the surface and apply a bonding agent before the next pour. For tall columns, pour in 2-foot lifts and vibrate each lift to eliminate air pockets.
How many bags of concrete for a 12-inch Sonotube?
A 12-inch diameter Sonotube uses approximately 1.3 bags of 80 lb concrete per linear foot. A 4-foot deep footing needs about 5-6 bags of 80 lb mix. Always buy 1-2 extra bags per column to account for the bell-shaped bottom and any spillage.
Should I use a bell footing at the bottom?
Bell footings (wider base) increase bearing capacity and are required by many codes. Dig the hole 6 inches wider than the tube at the bottom and pour concrete to fill before setting the tube. This creates a footing that resists uplift and spreads the load over more soil.