How to Calculate Post Hole Concrete
Hole volume: Pi x (Hole radius)^2 x Concrete depth
Post displacement: Post width^2 x Concrete depth (square post)
Concrete needed: Hole volume - Post displacement
Post Hole Guidelines
- Depth: 1/3 of total post length or below frost line (deeper wins)
- Diameter: 3x the post width (e.g., 12" hole for 4x4 post)
- Gravel: 4-6" of gravel at bottom for drainage
- Crown concrete: Slope top of concrete away from post for water runoff