Fence Post Spacing and Concrete Guide
Post spacing and footing depth determine whether a fence stands up or leans. Both decisions are made before the first post is set, and both are hard to change afterwards.
Spacing
| Fence type | Spacing | Notes |
|---|---|---|
| Privacy fence, 6 ft | 8 ft on center | The standard; heavy wind load |
| Privacy fence, 4 ft | 8–10 ft | Less sail area, can stretch |
| Picket fence | 8–10 ft | Light, less load |
| Vinyl privacy | 8 ft max | Vinyl is rigid; spacing must be consistent |
| Chain link | 10 ft | Line posts every 10, terminal posts at ends |
Always add a post at both ends and at every significant corner. A fence is only as strong as its end posts.
Footing depth
The footing must go below the local frost line — where the ground actually freezes. In most of the northern US that is 30 to 42 inches. In the south it may be as little as 15. Check your local building department; a wrong guess means a leaning fence.
For a 6 foot privacy fence in a cold climate, a 6 inch diameter hole at 42 inches deep is a reasonable starting point. Wide gates and end posts need bigger holes — a gate post carries the weight of the swing and needs to be the strongest post on the line.
How much concrete
About half a 60 lb bag per 4×4 post fills a standard 8–10 inch hole at typical depth. The rule that works: fill roughly one third of the hole with concrete. More is not better — concrete that is too rigid can lift the post out of the ground in a freeze.
Drainage matters more than depth. Slope the concrete away from the post and leave the top of the footing below grade so water runs off. Water pooling against the post is what rots it.
Setting posts straight
- Dig all the holes first, then set all the posts. Setting one at a time means the string line moves.
- Drive a string line at the height you want the top of the fence, with stakes at both ends.
- Plumb each post to the line. Check in both directions — a post can be plumb in one plane and leaning in the other.
- Brace each post before pouring.
- Pour concrete, and re-check plumb after it starts to set.
- Let it cure 48 hours before hanging rails.
The single most common fence mistake is setting posts one at a time without a level string line. The fence ends up with a visible wave along the top rail. Dig everything first, then level against one continuous string.
Post material
Pressure-treated posts in direct ground contact last 20+ years with a treated 6×6. Cedar and redwood last as long as anything but cost more. Steel posts outlast wood and avoid rot entirely, but they corrode unless powder-coated or hot-dip galvanized.
Whatever the material, use post bases — steel brackets that hold the post above grade. A 6×6 on concrete will sit in a puddle and rot from the bottom, even if the treated part is sound.
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