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Post Holes: How Many Bags of Concrete Mix Do I Need?

Make sure you have enough concrete for your project. These calculations help you estimate how many bags of concrete mix you need for setting posts.

Pouring Fast-Setting Concrete Mix into a Post Hole.

Calculating the Concrete Mix You Need

The tables below give you estimates for the number of 50- or 60-lb bags you need for several post and post hole sizes. Remember:

  • Before beginning any excavation, call 811 to check for underground utilities.
  • Moving and maneuvering bags of concrete mix takes significant effort. Enlist a helper.
  • Follow package instructions and cautions when working with concrete mix.
  • The calculations are estimates only. Your project needs may vary.

Estimating 50-lb Bags of Fast-Setting Concrete Mix

3-in Post Diameter / 9-in Hole Diameter   4-in Post Diameter / 12-in Hole Diameter   6-in Post Diameter / 18-in Hole Diameter
               
Hole Depth
in Inches
Number of Bags
needed Per Hole
  Hole Depth
in Inches
Number of Bags
needed Per Hole
  Hole Depth
in Inches
Number of Bags
needed Per Hole
10 1   10 2   10 4
12 1   12 2   12 4
14 2   14 2   14 5
16 2   16 3   16 5
18 2   18 3   18 6
20 2   20 3   20 6
22 2   22 3   22 7
24 2   24 4   24 7
26 2   26 4   26 8
28 3   28 4   28 9
30 3   30 4   30 10
32 3   32 5   32 10
34 3   34 5   34 10
36 3   36 5   36 11

Estimating 60-lb Bags of Fast-Setting Concrete Mix

3-in Post Diameter / 9-in Hole Diameter   4-in Post Diameter / 12-in Hole Diameter   6-in Post Diameter / 18-in Hole Diameter
               
Hole Depth
in Inches
Number of Bags
needed Per Hole
  Hole Depth
in Inches
Number of Bags
needed Per Hole
  Hole Depth
in Inches
Number of Bags
needed Per Hole
10 1   10 2   10 3
12 1   12 2   12 4
14 1   14 2   14 4
16 1   16 2   16 5
18 2   18 3   18 5
20 2   20 3   20 6
22 2   22 3   22 7
24 2   24 3   24 7
26 2   26 4   26 8
28 2   28 4   28 8
30 2   30 4   30 9
32 3   32 4   32 9
34 3   34 5   34 10
36 3   36 5   36 11