Fence Post Hole Calculator — Diameter, Depth & Volume
Size hole diameter, depth, and concrete volume for any fence post. Uses the 3× post-width rule for hole sizing and the one-third burial depth standard.
Enter Dimensions
Typically 1/3 of post height above grade
Results
Bags per Post
5bags
Total Bags
50bags
Volume per Hole
1.909cu ft
Concrete per post hole
Total Volume
19.09cu ft
All post holes combined
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
The hole sizes a fence post: diameter 3× the post width, depth below frost line and ≥ 1/3 the above-grade height. Get these two numbers wrong and your fence will heave, lean, or rot at the base within a season. This calculator returns both dimensions plus the concrete needed to fill the annular space around the post.
For per-post bag count, see the Fence Post Concrete Calculator. For depth-only analysis (frost line, 1/3 rule), see Fence Post Depth Calculator.
How to Size a Fence Post Hole
Diameter = 3 × Post Width. Depth = max(Above-Grade Height ÷ 3, Frost Line) + 4 in gravel. Hole Volume (cu ft) = π × (D÷24)² × Depth × 12.
Common Hole Sizes by Post and Fence Height
- 4×4 post, 4 ft fence: 10″ × 24″ deep hole = 1.09 cu ft total volume.
- 4×4 post, 6 ft fence: 10″ × 32″ deep hole = 1.45 cu ft.
- 6×6 post, 6 ft fence: 14″ × 36″ deep hole = 3.21 cu ft (gate post or corner).
- 4×4 post, 8 ft fence: 12″ × 42″ deep hole = 2.75 cu ft.
- Frost-zone correction: in MN/ND/ME, dig to 48-60 inches regardless of post height.
Frequently Asked Questions
What is the right size for a fence post hole?
Diameter = 3 × post width (4×4 post needs 10-12 inch hole; 6×6 needs 16-18 inch). Depth = the greater of (1) one-third of the above-grade post height, and (2) the local frost line depth, plus 4 inches of gravel.
How deep does a fence post hole need to be?
For a 6 ft tall fence, plan a minimum 24-inch hole — 8 inches above frost in southern zones and well below frost in northern climates. Posts seated shallower than 1/3 of above-grade height will lean within a year.
Should I dig wider or deeper for stability?
Deeper. Lateral stability comes more from depth than diameter. A 36-inch deep × 10-inch wide hole resists tipping better than a 24-inch deep × 14-inch wide hole using the same amount of concrete.
Can I use a hand digger or do I need an auger?
Manual post-hole diggers work for 6-10 holes in soft soil. For 10+ holes or clay/rocky soil, rent a two-person gas auger ($60-90/day) or hire a fence contractor with a hydraulic auger.
Do I need gravel in the bottom of the hole?
Yes — 3-4 inches of compacted crushed stone at the bottom of every post hole provides drainage that significantly extends post life. Without drainage, water pools at the post base and causes early rot in wood posts.
Looking for the general calculator?
Calculate how many bags of concrete you need per fence post hole. Supports 4×4 and 6×6 wood posts plus metal pipe posts in standard hole sizes.
Open the Concrete Fence Post Calculator: Bag Count →