How Deep Should Fence Posts Be?
A good rule of thumb is to bury fence posts about one-third to one-half of the fence’s above-ground height, with a minimum of 24 inches. In cold climates, the bottom of the hole should also sit below your local frost line so freezing soil can’t push the post up.
Quick Calculator
Posts
16
Concrete
32
Pickets
320
Rails
39
Est. Cost
$1,500–$2,500
Detailed Answer
Typical post depths and post lengths to buy: - 3–4 ft fence: 24 in deep → 6 ft posts - 5 ft fence: 24–30 in deep → 7–8 ft posts - 6 ft fence: 24–36 in deep → 8 ft posts (or 9–10 ft for deeper holes) - 8 ft fence: 36–48 in deep → 10–12 ft posts
Hole width: about 3 times the post width. That is 10–12 inches for a 4×4 and 14–16 inches for a 6×6.
Frost line: in cold climates the frost line can be 36 inches or deeper. Your local building department can tell you the required depth.
Add 4–6 inches of gravel at the bottom of each hole for drainage before setting the post.
Recommended Materials
Pressure-Treated Fence Post 4×4×8
Ground-contact rated, ideal for all fence types.
$12 – $18
Cedar Dog-Ear Picket 1×6×6
Naturally rot-resistant, smooth on one side.
$3 – $6
Quikrete 60 lb Fast-Setting Concrete
Sets in 20-40 minutes. No mixing required.
$5 – $7
Post Hole Digger – Fiberglass Handle
Heavy-duty clamshell digger for clean holes.
$35 – $55
Simpson Strong-Tie Fence Bracket
Galvanized L-bracket for rail-to-post connections.
$4 – $8
Decorative Post Cap 4×4
Copper-top cap, fits standard 4×4 posts.
$5 – $12