Guides / Fences and walls · Updated
Fence post spacing and depth
Depth rules from Quikrete's post setting instructions. In cold country, the frost line can mean digging deeper.
Short answer
Space wood fence posts 8 ft on center. Go 6 ft if it's windy. Bury the post a third as deep as the fence is tall, so 24 in for a 6 ft fence. Dig 6 in deeper for gravel, which makes the hole 30 in.
How far apart
8 ft is standard. Rails come in 8 ft lengths, so each one spans a section with no cutting. At 6 ft you cut the rails down, and you buy more posts. In return the fence is stiffer in wind.
| Straight run | Posts at 8 ft | Posts at 6 ft |
|---|---|---|
| 50 ft | 8 | 10 |
| 100 ft | 14 | 18 |
| 150 ft | 20 | 26 |
| 200 ft | 26 | 35 |
Posts = total fence length ÷ spacing, rounded up, plus 1. Add one for every corner and one for every gate.
How deep should a fence post be?
A third of the fence height, plus 6 in of gravel under it. So a 6 ft fence post goes 24 in into the ground in a 30 in hole, and a 4 ft one goes 16 in. The gravel lets water drain out of the bottom so the post doesn't rot.
| Fence height | Post in the ground | Hole depth | Post to buy |
|---|---|---|---|
| 4 ft | 16 in | 22 in | 6 ft |
| 5 ft | 20 in | 26 in | 8 ft |
| 6 ft | 24 in | 30 in | 8 ft |
| 8 ft | 32 in | 38 in | 12 ft |
Hole depth includes 6 in of gravel. Post length is height plus the buried part, rounded up to the next stock length.
Most towns cap backyard fences at 6 ft. An 8 ft fence usually takes a permit or a variance, so call before you buy.
How wide
Make the hole 3 times the post's width. That leaves room for concrete all the way around.
| Post | Actual width | Hole across |
|---|---|---|
| 4x4 Most fences | 3.5 in | 10.5 in |
| 6x6 Gates, tall or windy | 5.5 in | 16.5 in |
Stop the concrete 3 in below grade, so you can cover it with dirt or sod.
Gate posts and frost
Gate posts take the most beating. Go 6x6, or set them 6 in deeper than the line posts. A 6 ft fence's gate posts go 30 in. Put a brace on every gate.
Where the ground freezes, the hole goes below the frost line. If yours is deeper than the table, dig to it and buy longer posts. Your building department knows the local depth, and the frost line depth by state guide gives you a ballpark.
Before you dig
Call 811 a few days before you dig. Every post hole is a chance to hit a gas line, and the locate is free.