How Deep Should Fence Posts Be? Depth Calculator & Chart
Independent research · Last reviewed
The short answer
Set fence posts at least one third of the fence's above-ground height deep, and no less than 24 in for a 4 ft fence, 30 in for a 6 ft fence and 36 in for an 8 ft fence. Wherever your local frost line is deeper, go to the frost line instead: 42–60 in across much of the North. Set gate and corner posts deeper or wider still.
6 ft wood fence
Line post hole depth
30 in
Set by the minimum for this fence height, which is deeper than one third of its height.
One third: 24 in · Minimum: 30 in · Frost: none
Gate & corner posts
36 in
Post length to buy
9 ft
Hole width
10.5 in
Concrete per post
4 × 50 lb
No frost depth applied. Enter a zip or pick a state if the ground freezes where you are; see frost line depth by zip code.
Planning figures only. Frost depth is set by your local building department, and it is the legal number — confirm before you dig.
Fence post depth chart by height and frost line
Find your fence height in the left column and your frost depth across the top. The cell is the hole depth for a line post; shaded cells are where the frost line, not the height, sets it.
| Fence height | No frost | 12 in frost | 24 in frost | 30 in frost | 36 in frost | 42 in frost | 48 in frost | 60 in frost | Post to buy (no frost) |
|---|---|---|---|---|---|---|---|---|---|
| 3 ft | 24 in | 24 in | 24 in | 30 in | 36 in | 42 in | 48 in | 60 in | 6 ft |
| 4 ft | 24 in | 24 in | 24 in | 30 in | 36 in | 42 in | 48 in | 60 in | 6 ft |
| 5 ft | 30 in | 30 in | 30 in | 30 in | 36 in | 42 in | 48 in | 60 in | 8 ft |
| 6 ft | 30 in | 30 in | 30 in | 30 in | 36 in | 42 in | 48 in | 60 in | 9 ft |
| 7 ft | 36 in | 36 in | 36 in | 36 in | 36 in | 42 in | 48 in | 60 in | 10 ft |
| 8 ft | 36 in | 36 in | 36 in | 36 in | 36 in | 42 in | 48 in | 60 in | 12 ft |
Shaded: set by the frost line. Unshaded: set by the height minimum. Post length assumes no frost; add the extra depth where frost governs, or use the calculator above.
Which rule sets your depth
Three numbers compete, and the deepest wins. One third of the above-ground height is the familiar rule of thumb. The height minimum (24 / 30 / 36 in for 4 / 6 / 8 ft) is deeper than one third at every height up to 8 ft, so it is what actually sets a residential post. The frost depth overrides both wherever the ground freezes deeper. For a 6 ft fence:
- Georgia (12 in adopted): 30 in, set by the height minimum.
- Ohio (30–36 in adopted): 36 in, set by the frost depth.
- Minnesota (42–60 in adopted): 60 in, set by the frost depth.
Taller and solid fences catch more wind, which is why the minimum rises with height. In loose sand or on an exposed site, going deeper than the chart costs little and helps.
Post depth by fence type
| Fence type | Posts (line / corner & gate) | Hole width | Depth, 4 ft | Depth, 6 ft | Set in |
|---|---|---|---|---|---|
| Wood privacy / picket | 4x4 wood (3.5" actual) / 4x4 wood (3.5" actual), 6 in deeper | 10.5 in | 24 in | 30 in | Concrete |
| Vinyl panels | 5x5 vinyl sleeve / 5x5 vinyl sleeve | 12 in | 24 in | 30 in | Concrete |
| Chain link | 2⅜" round steel (chain link line post) / 2⅞" round steel (chain link terminal post) | 9.5 in | 24 in | 30 in | Concrete |
| Split rail | 6x6 wood (5.5" actual) / 6x6 wood (5.5" actual) | 16.5 in | 24 in | 30 in | Tamped gravel & soil |
| Woven / field wire on T-posts | Driven T-posts / 6x6 wood (5.5" actual) | 16.5 in | 24 in | 30 in | Concrete |
| Barbed wire on T-posts | Driven T-posts / 6x6 wood (5.5" actual) | 16.5 in | 24 in | 30 in | Concrete |
Depths are for ground that doesn't freeze; frost overrides them all. Chain link uses a heavier round post at every end, corner and gate, in a hole four times its diameter, so a 4 ft chain link fence takes 24 in line holes 9.5 in wide (chain link fence calculator). Wire fences drive their line posts and set only the braced corner and gate posts in holes. Hole sizes and terminal depths follow the installation sources cited in the post calculator.
The frost line overrides the rule
Water in freezing soil expands, and a footing that sits in the frozen layer gets lifted a little each winter without fully settling back. Over a few seasons that is how a straight fence starts to wave, and more concrete doesn't help, because the concrete is what's being lifted.
Frost depth is a local code figure, not a weather reading. Adopted depths run from none in Florida and Hawaii to 60 in across the far North, and IRC R403.1.4 keeps footings at least 12 in below grade regardless. Look up frost line depth by zip code or see the frost line depth by state.
Planning figures only. Frost depth is set by your local building department, and it is the legal number — confirm before you dig.
Hole width and concrete per post
Dig the hole three times the post's width for square posts, and four times the diameter for round posts up to 4 in (ASTM F567). Concrete per post at 30 in deep, with the post's volume taken out and 10% added for an uneven hole:
| Post | Hole | 50 lb bags | 80 lb bags |
|---|---|---|---|
| 4x4 wood (3.5" actual) | 10.5 in | 4 | 3 |
| 6x6 wood (5.5" actual) | 16.5 in | 10 | 6 |
| 2⅜" round steel (chain link line post) | 9.5 in | 4 | 3 |
For the whole fence, use the fence post calculator.
Concrete or gravel?
Concrete gives the most rigidity, which matters for gates and in high wind. Its weakness is that a collar can hold water against a wood post and speed up rot, unless the top is crowned so water runs away from the wood.
Gravel drains freely, keeps the post base drier and makes replacing a post years later far easier, at some cost in stiffness. Done properly it is more work, not less: dig about three times the post width to the full depth, backfill with coarse angular gravel (pea gravel rolls and never locks), tamp in 4–6 in layers, and crown the top.
Use concrete anyway on gate, corner and end posts, tall solid privacy fences, windy sites and soft or sandy soil. A sensible mix is gravel on the line posts and concrete where the force is. What doesn't work is a narrow hole backfilled with loose native soil, which is the most common reason a new fence moves by its second winter.
What the post should be made of
The post is the part that fails, and it doesn't have to match the fence.
| Post | Typical life | The trade |
|---|---|---|
| Pressure-treated wood | 10–20 yr | The default. Check it is rated for ground contact — the lighter above-ground grade is often what gets delivered, and it rots fast in a hole. |
| Cedar | 10–15 yr | Excellent above grade, unremarkable below it. Matching panels to posts looks best and lasts least. |
| Galvanised steel | 30–50 yr | Outlives the panels it carries. Systems exist that take standard wood rails and hide the post behind a board, which is how you get steel life with a timber fence. |
| Concrete / precast | 40 yr + | Effectively permanent and heavy to handle. Common in the UK, uncommon in US residential work, and visually assertive. |
| Vinyl-sleeved | 20–40 yr | A vinyl shell over a wood or steel core. The sleeve does not carry load — what is inside it does, so ask. |
Wood posts rot in a narrow band at and just below ground level, where moisture and oxygen meet, so coatings on the buried end miss the zone that matters. Ground-contact-rated wood, drainage under the post and a crowned footing do more. Panel-side costs are in wood fence costs.
What this calculator doesn't tell you
- Soil. Loose sand and wet clay hold a post less well; go deeper or wider there.
- Wind. Solid panels load posts far more than open fences; closer spacing helps as much as depth.
- Slopes. Measure depth from the low side of the hole — see posts on a slope.
- Local code. Your building department's frost depth is the legal number.
- It's invisible later. Post depth can't be checked once the fence is up, so get post depth in writing and check your quote.
Call 811 before digging. It's free, generally required, and post holes are deep enough to reach buried utilities.
Local rules vary. Frost depth and post-depth requirements are local. Confirm with your building department — these are planning figures, not a code specification. Deck footings follow their own rules: see deck footing depth.
Frequently asked questions
- What is the proper depth for a fence post?
- At least a third of the above-ground height, and no less than 24 / 30 / 36 in for a 4, 6 or 8 ft fence. Where your frost line is deeper, go to the frost line.
- How deep should a fence post be for a 6 ft fence?
- 30 in where frost is shallow; your frost depth where it is deeper — 36 in in Ohio, 48 in in Massachusetts and Wisconsin, 42–60 in in Minnesota by zone.
- How deep should a 4 ft chain link fence post be?
- 24 in where frost is shallow, or your frost depth if deeper. Line posts in a 9.5 in hole, terminal posts in a 11.5 in hole. Check the manufacturer's instructions too.
- What size hole for a 2 3/8 fence post?
- About 9.5 in — four times the post diameter, the ASTM F567 rule for round posts up to 4 in.
- How many 50 lb bags of concrete per fence post?
- A 4x4 in a 10.5 in hole takes about 4 bags at 30 in and 5 at 36 in, 10% waste included. The calculator above works it out for your post.
- Should fence posts be set in concrete?
- Not always. Use concrete on gate, corner and end posts, tall solid fences and soft soil; tamped coarse gravel drains better elsewhere. Same depth either way, with a crowned top.
- How deep should a fence post be in Ohio?
- Ohio commonly adopts 30–36 in, so plan a 36 in hole for a 6 ft fence. See Ohio's frost line and confirm locally.
- Is fast-setting concrete good for fence posts?
- Fine for line posts. The 20–40 minutes on the bag is initial set, not strength — wait a day or two before hanging panels or a gate, and mix it properly for gate and corner posts.
- How do I get an old concrete footing out?
- Lever it out, jack it out with a chain on the stub, or break it up in place — or set the new post alongside where an offset won't show. It is the biggest variable in post replacement cost.