Column & Post Hole Calculator

Calculate concrete for round columns, square columns, post holes, and piers.

Column Details
Per Column
0.33
cubic feet each
Total Volume
1.44 cu ft
Cubic Yards
0.053
80lb Bags
3 bags
60lb Bags
4 bags
Common Sonotube Sizes — Bags Needed (80lb at 48" deep)
DiameterCommon UseVolume/Column80lb Bags/Column
6"Mailbox, Light Post0.08 cu ft1 bag
8"Fence Post0.14 cu ft1 bag
10"Deck Post0.22 cu ft1 bag
12"Deck Pier, Porch0.31 cu ft1 bag
16"Large Deck, Pergola0.56 cu ft1 bag
24"Heavy Structure1.26 cu ft3 bags

How to Pour Concrete Columns

  1. Dig the hole to the required depth (below frost line for structural posts)
  2. Add 4" of gravel at the bottom for drainage
  3. Set the Sonotube level and brace it plumb
  4. Mix and pour concrete in 8" lifts, tapping sides to release air bubbles
  5. Set the post bracket or anchor bolt before concrete hardens
  6. Cure for 24-48 hours before attaching anything