Construction & Home
Fence Post Concrete Calculator
Get the right number of 60 lb or 80 lb bags per fence post hole. Sizes for 4×4, 6×6, and round posts at any depth.
in
4×4 actual = 3.5 in
in
in
Post layout · cross-section
Bags per post
5
60 lb bag
Total 60 lb bags
47
Includes 10% waste
Cubic feet total
21.01
How this is calculated
For each post hole, concrete fills the cylinder of the hole minus the cross-section of the post itself:
volume per hole = (π · r_hole² − r_post²) × depth
Rules of thumb
- Hole depth = 1/3 the above-ground post height + 6 in below frost line.
- Hole diameter = 3× post width (4×4 post → 12 in hole).
- For a 6 ft fence with 4×4 posts: 12 in dia × 30 in deep → ~2 bags of 60 lb concrete per post.
- Always crown the top to shed water away from the post.
Frequently asked
- Generally 1/3 the height of the post above ground, plus 6 in below frost line. For a 6 ft fence: 24–36 in deep.