Fence Post Concrete Calculator
A standard 4x4 fence post hole (10 in diameter, 36 in deep) needs about 3 bags of 80-lb concrete mix — a typical 10-post fence run needs roughly 30 bags total, about 0.6 cubic yards. Enter your hole size, depth, and post count below for an exact bag count. Gate and corner posts typically need larger holes — a 16-in by 42-in hole takes about 9 bags each.
Pro Tips
- →Space line posts 6-8 ft apart for standard fence panels
- →Hole diameter should be 3x the post width (4x4 = 10-12 in, 6x6 = 16-18 in)
- →Gate and corner posts need larger, deeper holes to handle extra load
- →Extend below the frost line in cold climates to prevent heaving
- →Use fast-setting mix: pour the dry mix into the hole, then add water
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.
44 bags × 80lb
0.96 cubic yards + delivery
Prices vary by location and time. Contact local suppliers for accurate quotes.
For general step-by-step instructions, read our complete Concrete Fence Post Guide and Concrete Mailbox Post.
Fence Post Concrete: How Much You Need
For a standard 4x4 wood or vinyl fence post, dig a hole about 3 times the post's width — roughly 10 inches for a 3.5-in actual 4x4 — and 30-36 inches deep, extending below your local frost line. A 10-in x 36-in hole holds about 1.64 cubic feet of concrete, which works out to roughly 3 bags of 80-lb fast-setting mix per post after the standard 10% waste allowance. A typical residential run of 10 posts needs about 30 bags total, around 0.6 cubic yards. For the general math behind any hole size, see the Post Hole Calculator.
Post Spacing and Post Size
Line posts on a standard wood or vinyl fence are spaced 6 to 8 feet apart to match common panel and rail lengths — tightening spacing below 6 ft rarely saves concrete since bag counts round to whole numbers anyway. Post size scales with the load: 4x4 posts (3.5 in actual) handle most residential line runs, while 6x6 posts (5.5 in actual) go on gates, corners, and tall privacy fences that catch more wind. Because hole diameter should track about 3x the post width, a 6x6 wants a 16-18 in hole rather than the 10-12 in hole that suits a 4x4.
| Post | Actual Width | Hole Diameter | Depth | 80-lb Bags |
|---|---|---|---|---|
| 4x4 line post | 3.5 in | 10 in | 36 in | 3 |
| 4x4 line post (deep frost) | 3.5 in | 10 in | 42 in | 3 |
| 6x6 gate/corner post | 5.5 in | 16 in | 42 in | 9 |
Gate Posts, Corner Posts, and Wind Load
Gate and corner posts carry more than their own weight — a swinging gate levers against its post every time it opens, and corner posts anchor the tension of the whole fence line. Both should go one size up in hole diameter and several inches deeper than the line posts around them, ideally paired with a 6x6 or larger post. Taller privacy and wind-screen fencing multiplies wind load on every post along the run, which is another reason to widen and deepen holes rather than relying on post strength alone.
Frost Line and Fast-Setting Mix
Extend every hole below your local frost line — as shallow as 6 in in the Deep South, 42-60 in across the northern Midwest and New England — so freeze-thaw heaving can't push posts out of plumb over time. For the pour itself, fast-setting mix is the standard choice for fence posts: brace the post plumb, pour the dry mix into the hole around it, then add water and let it set in 20-40 minutes with no premixing. Quikrete and Sakrete fast-setting formulas perform almost identically for this job; see Quikrete vs. Sakrete vs. Generic for the side-by-side. If you're setting load-bearing deck posts rather than fence posts, use the Deck Footing Calculator instead — footing sizing follows structural load, not the simple 3x-width rule.