Fence Post Depth Calculator
A fence is only as strong as what you can't see. Enter your fence height and climate for the exact burial depth, the hole depth to dig, and the post length to buy. Free, instant, no signup.
Quick answer
Bury fence posts at the greatest of: frost line + 6 in, one-third of the fence height, or 24 in minimum. A 6-foot fence lands at 24–36 in deep; gate and corner posts go 6 in deeper. In the Northeast and upper Midwest, the frost line — not the rule of thumb — decides.
Your fence post depth
Bury the post
24 in deep
2 ft below grade — set by the one-third rule
- Hole depth to dig (incl. 6 in gravel base)
- 30 in
- Post length to buy
- 8 ft (standard size)
- Exact post length needed
- 8 ft
- Hole diameter (≈3× post width)
- 12 in
Depths follow the guide's formula: the greatest of frost line + 6 in, one-third of the fence height, or 24 in. Local building code always wins — your building department publishes the exact frost depth for your zip code. Call 811 before you dig.
How the calculation works
- Three candidate depths: frost line + 6 in, one-third of the above-ground height, and the 24 in hard minimum.
- The greatest wins. In warm climates the one-third rule or the minimum usually controls; where winters freeze the ground, the frost line overrides everything.
- Gate and corner posts get +6 in — they carry swinging, twisting loads, not just panels.
- The hole is dug 6 in deeper than the post depth (gravel drainage base) and about 3× the post width across, so concrete can cradle the post.
Depth chart by fence height
| Fence height | Typical depth | Notes |
|---|---|---|
| 4 ft | 16–24 in | Check the frost line first |
| 5 ft | 20–30 in | Mind wind exposure |
| 6 ft | 24–36 in | Privacy panels catch wind like a sail |
| 7 ft | 28–42 in | Check local height rules |
| 8 ft | 32–48 in | Permit territory; larger posts |
Why the frost line beats every rule of thumb — and how frost heave lifts shallow posts out of the ground — is covered in our fence post depth guide. Spacing the posts along the run? See the fence post spacing guide.
Worked example: one 6-foot fence, two climates
A standard 6-ft privacy fence on 4×4 posts shows why this calculator asks about your climate before it gives you a number:
- Warm climate, no frost: the one-third rule governs — bury a third of the post. The hole is 24 inches deep, and an 8-ft post gives you exactly 6 ft above ground and 2 ft below.
- Cold climate, 36-inch frost line: the post must sit below the frost line, so the hole goes to 42 inches deep. Now the post has to be 6 ft above ground plus 3.5 ft below — 9.5 ft, which means buying 10-ft posts.
- Gate posts, either climate: add 6 inches more depth. Gates hang, swing, and slam; their posts earn the extra concrete and depth.
Same fence, same lumber aisle — the climate changed both the digging and the shopping list.
Mistakes that throw off the estimate
- Following the one-third rule and ignoring frost. In cold country, frost heave lifts shallow posts a little every winter until the fence line waves. When the two rules disagree, the deeper one wins.
- Measuring from the wrong ground level. If the yard slopes — or you'll add soil, mulch, or a patio later — the finished grade changes how much post is really above ground. Measure from the lowest finished level the post will see.
- Setting a solid fence like an open one. A solid privacy fence catches wind like a sail, and a 6-ft solid panel loads its posts far harder than spaced pickets do. Tall and solid means the deep end of every range.
- Digging before you call. In the US, call 811 a few days before you dig so buried lines get marked — it's free, and a struck utility line costs more than the entire fence.