Concrete Post Hole Calculator
A standard fence post hole (10 in diameter, 36 in deep) needs about 3 bags of 80-lb concrete — 8 posts need roughly 22 bags total. Enter your hole size, depth, and quantity below to get the exact count.
Pro Tips
- →Post holes should be 3 times the post width
- →Depth should be 1/3 to 1/2 the above-ground height
- →Extend below frost line in cold climates
- →Use fast-setting concrete mix for posts
- →Add gravel at bottom for drainage
Includes 10% waste factor
That's typically a professional pour. See costs ↓
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Cost Estimate
Estimated material costs for your project
Recommendation: Bagged Concrete
For smaller projects, bagged concrete gives you more control and less waste.
35 bags × 80lb
0.77 cubic yards + delivery
Prices vary by location and time. Contact local suppliers for accurate quotes.
For general step-by-step instructions, read our complete How Many Bags and How To Mix Concrete.
Post Hole Sizing Guide
Post hole diameter should be 3 times the post width — a 4×4 post needs a 10–12 inch diameter hole, a 6×6 post needs a 14–18 inch hole. Depth depends on frost line depth and above-ground post height: the bottom of the hole must reach below the local frost line, and should be at least 1/3 to 1/2 the above-ground post height.
| Post Size | Hole Diameter | Typical Depth | Bags (80-lb, incl. waste) |
|---|---|---|---|
| 4×4 post | 10–12 in | 30–36 in | 2–3 bags |
| 4×4 post | 10–12 in | 42–48 in | 3–4 bags |
| 6×6 post | 14–16 in | 36–42 in | 4–6 bags |
| 6×6 post | 14–16 in | 48–60 in | 6–9 bags |
Fast-Setting vs. Standard Concrete
For fence posts and most deck posts, fast-setting concrete (Quikrete Fast-Setting Concrete Mix or equivalent) is the standard choice. Pour the dry mix into the hole around the post, add water, and the concrete sets in 20–40 minutes — no premixing required. You can set an entire fence line in a single day.
Standard concrete requires mixing first and takes 24–48 hours to reach working strength. Use it when post positions may need adjustment, or when you need the longer working time that fast-set doesn't allow.
Frost Line Depths by Region
In cold climates, post holes must extend below the frost line — the depth at which soil freezes in winter. Footings above the frost line will heave seasonally, tilting posts out of plumb over time.
| Region | Frost Line Depth |
|---|---|
| Deep South (FL, LA, TX coast) | 0–6 in |
| Mid-Atlantic, Pacific Coast | 12–24 in |
| Midwest, Upper South | 30–42 in |
| Northern states (MN, WI, ME) | 42–60 in |
Always verify the required depth with your local building department — frost depths in building codes are authoritative, and deck permit inspections check footing depth.
Setting Posts Correctly
- Add 3–4 inches of gravel at the hole bottom for drainage
- Set the post, check plumb in two directions, and brace temporarily
- Pour concrete around the post to 2 inches below grade
- Dome the top surface to shed water away from the post base
- Hold braces for 4 hours (fast-set) or 24 hours (standard mix) before loading
For cylindrical tube-form footings (sonotubes), see our Sonotube Calculator. For structural deck footings, use the Deck Footing Calculator.