Concrete Column Calculator
Short answer: volume = π × (diameter ÷ 2)² × height. A 12 in diameter, 4 ft high column holds about 0.12 cubic yards — three of them need 0.35 cubic yards — enter your columns below.
Calculate your columns
How the calculation works
Each column is a cylinder: volume = π × radius² × height, with diameter and height in feet. Multiply by the number of identical columns, then divide cubic feet by 27 for cubic yards.
Worked example: one 12 in diameter column, 4 ft high = π × (0.5 ft)² × 4 ft = 3.14 cu ft = 0.12 cubic yards. Three of them = 0.35 cubic yards (0.38 with 10% waste).
Common column sizes (one column, 4 ft high)
| Diameter | Volume | 80 lb bags |
|---|---|---|
| 8 in | 0.05 cubic yards | 3 |
| 10 in | 0.08 cubic yards | 4 |
| 12 in | 0.12 cubic yards | 6 |
| 16 in | 0.21 cubic yards | 10 |
| 18 in | 0.26 cubic yards | 12 |
Volumes are net (before waste). Bag counts use the 0.60 cu ft yield per 80 lb bag, rounded up.
Frequently asked questions
How much concrete for a 12 inch sonotube?
A 12 inch diameter tube 4 ft high holds 0.12 cubic yards net — about 6 × 80 lb bags including 10% waste.
How do you calculate concrete for a round column?
Volume = π × (diameter ÷ 2)² × height, all in feet, then divide by 27 for cubic yards. Multiply by the number of identical columns.
How many bags for one fence post hole?
A 12 inch hole 3 ft deep needs about 0.09 cubic yards net — 4 × 80 lb bags, or 5 allowing for the extra waste hand-dug holes usually need.