Concrete Column & Pier Calculator

How to Calculate Concrete for Sonotubes & Columns

Sonotubes (cardboard form tubes) are the standard method for pouring round concrete piers for decks, porches, and post foundations. Getting the volume right saves you from mixing extra bags or making emergency supply runs.

The Column Volume Formula

Volume = π × (Diameter ÷ 24)² × Height. This gives cubic feet per column. Multiply by the number of columns, then divide by 27 to convert to cubic yards.

Example: Four 12" diameter tubes at 4 ft tall = π × 0.25 × 4 × 4 = 12.57 cu ft ÷ 27 = 0.47 cubic yards (about 21 bags of 80 lb Quikrete).

When to Use Sonotubes

• Deck footings — Most common use; supports deck posts at or below grade
• Porch columns — Foundation piers for covered porch structures
• Fence post footings — Heavy-duty posts for gates and corners
• Sign and light pole bases — Commercial and residential
• Structural columns — Load-bearing supports for additions

Frost Line Depths by Region

• Southern US (FL, TX, AZ) — 0"–12" frost line, 12"–18" minimum pier depth
• Mid-Atlantic (VA, NC, TN) — 12"–24" frost line, 24"–30" minimum pier depth
• Midwest (IL, OH, IN) — 30"–42" frost line, 42"–48" minimum pier depth
• Northern US (MN, WI, ME) — 42"–60" frost line, 48"–60"+ minimum pier depth
• Always check your local building code — frost depth varies significantly even within regions

Common Column Sizes for Decks

• 8" diameter — Lightweight deck posts, low load applications
• 10"–12" diameter — Standard residential deck piers, most common size
• 14"–16" diameter — Multi-story decks, heavy snow load regions
• 18"–24" diameter — Commercial applications, heavy structural loads
• Larger diameters spread load over more soil area — important for poor-bearing soils