Most fence failures start at the posts: too shallow, too small, too far apart, or rotted at the ground line. This guide gives the usual rules for how deep to set fence posts, how far apart to space them, what size to use, how much concrete each hole takes, and the spacing rules for pickets around pools. It is for wood and chain link fences around a home; farm fencing for livestock follows different practice. For materials, use the fence calculator and the post hole concrete calculator.
How deep to set fence posts
- Rule of thumb: bury at least one third of the post’s total length, and not less than 2 ft. A 6 ft fence on 8 ft posts gives 2 ft in the ground; many builders use 10 ft posts with 3 ft buried for solid privacy fences, which catch the wind like a sail.
- Frost: in cold climates, setting the bottom of the post and its concrete below the local frost depth reduces heaving, where freezing soil lifts the post a little each winter. Your building department publishes the frost depth used for footings in your area.
- Soil: sand and soft or wet clay need deeper holes or wider footings than firm, well-drained soil.
- Gates: gate posts carry a twisting load; set them deeper and larger than line posts, often 6×6 for wide or heavy gates.
- Utilities: call 811 (in the US) a few working days before you dig so buried lines are marked.
Hole size and concrete per post
| Hole diameter | Depth | Post | Concrete | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 8 in | 24 in | 4×4 | 0.53 cu ft | 1 | 2 |
| 8 in | 30 in | 4×4 | 0.66 cu ft | 2 | 2 |
| 8 in | 36 in | 4×4 | 0.79 cu ft | 2 | 2 |
| 10 in | 24 in | 4×4 | 0.92 cu ft | 2 | 3 |
| 10 in | 24 in | 6×6 | 0.67 cu ft | 2 | 2 |
| 10 in | 30 in | 4×4 | 1.15 cu ft | 2 | 3 |
| 10 in | 30 in | 6×6 | 0.84 cu ft | 2 | 2 |
| 10 in | 36 in | 4×4 | 1.38 cu ft | 3 | 4 |
| 10 in | 36 in | 6×6 | 1.01 cu ft | 2 | 3 |
| 12 in | 24 in | 4×4 | 1.40 cu ft | 3 | 4 |
| 12 in | 24 in | 6×6 | 1.15 cu ft | 2 | 3 |
| 12 in | 30 in | 4×4 | 1.75 cu ft | 3 | 4 |
| 12 in | 30 in | 6×6 | 1.44 cu ft | 3 | 4 |
| 12 in | 36 in | 4×4 | 2.10 cu ft | 4 | 5 |
| 12 in | 36 in | 6×6 | 1.73 cu ft | 3 | 4 |
A common guide is a hole about three times the width of the post: 10 to 12 in for a 4×4 and 16 to 18 in for a 6×6, wide enough for a collar of concrete all round. Put a few inches of gravel in the bottom so water drains away from the end grain, and slope the top of the concrete so water runs off rather than pooling against the post. Some builders prefer packed gravel instead of concrete for wood posts in well-drained soil, which drains better and makes posts easier to replace.
How far apart to space fence posts
- Wood privacy and picket fences: 6 to 8 ft on centre. 8 ft is standard because rails are cut from 8 ft lumber; 6 ft spacing makes a stiffer fence in windy areas or with heavy boards.
- Chain link: line posts are commonly up to about 10 ft apart, with heavier terminal posts at ends, corners and gates.
- Lay out from the ends: set corner and end posts first, run a string line, and divide the run into equal bays no wider than your maximum spacing rather than ending with one short bay.
Example: a 100 ft run at a maximum of 8 ft needs 100 ÷ 8 = 12.5, rounded up to 13 bays, so 14 posts at 7 ft 8-5/16 in on centre. The fence calculator does this for any length and adds rails, pickets and concrete.
Post size
For residential wood fences up to 6 ft, 4×4 posts (3-1/2 in actual) are the norm, and 6×6 posts (5-1/2 in) are used for gates, corners, taller fences and solid fences in exposed, windy sites. Buy posts rated for ground contact if they are treated, and set the treated end in the ground; cut ends above ground can be sealed with a preservative. See the lumber dimensions chart for actual sizes.
Which wood lasts in the ground
Untreated wood in contact with soil rots fastest at the ground line, where it is both wet and exposed to air. The USDA Wood Handbook rates the heartwood of these North American softwoods resistant to decay: Atlantic white cedar, Eastern redcedar, Incense cedar, Northern white-cedar, Port-Orford cedar, Redwood (old-growth), Western redcedar, Yellow-cedar (Alaska). Among hardwoods, black locust is rated very resistant, and white oak and several other white oaks resistant. Sapwood of every species has low decay resistance, so untreated posts need to be mostly heartwood; for most fences, pressure-treated posts rated for ground contact are the practical choice.
Picket spacing and pool barriers
- Privacy fences: butt boards together, or overlap them board-on-board so no gap opens as they shrink. Green treated boards can shrink by 3/16 in or more across the width (see our deck board spacing guide for the arithmetic).
- Spaced picket fences: no general code gap; a gap about equal to or a little less than the picket width is a common look. Many towns limit fence height and set rules for front yards and corners, so check local zoning before you build.
- Pool barriers: a fence that serves as a swimming pool barrier must be at least 48 in high and is covered by the pool barrier rules in the International Swimming Pool and Spa Code (Section 305), formerly IRC Appendix G. Openings must not let a 4 in sphere pass, and where the horizontal rails are less than 45 in apart (so the rails could be climbed), vertical members may be no more than 1-3/4 in apart. Gates must be self-closing and self-latching. Check the edition your jurisdiction has adopted.
Frequently asked questions
How deep should a fence post be for a 6 ft fence?
At least 2 ft, which is one third of an 8 ft post, and deeper (often 3 ft) for solid privacy fences, gates, soft soil and cold climates where posts should reach below the frost depth.
How far apart should fence posts be?
6 to 8 ft on centre for wood fences, 8 ft being standard with 8 ft rails. Chain link line posts are commonly up to about 10 ft apart.
How many bags of concrete per fence post?
For a 4×4 post in a 10 in hole 24 in deep, about 0.9 cu ft of concrete: two 80 lb bags or three 60 lb bags. See the table for other sizes.
What is the code for fence picket spacing?
There is no general building code gap for ordinary fences. Pool barriers are the exception: openings must not pass a 4 in sphere, and vertical members can be at most 1-3/4 in apart where rails are less than 45 in apart.
Sources
- International Code Council, International Swimming Pool and Spa Code (ISPSC), Section 305 barrier requirements (previously IRC Appendix G), paraphrased; local adoption varies.
- QUIKRETE Concrete Mix product data: about 0.60 cu ft per 80 lb bag and 0.45 cu ft per 60 lb bag.
- USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (2010), Table 14-1, heartwood decay resistance.
- Post depth, hole size and spacing: common residential fencing practice, summarised; follow your local code, zoning and the post maker’s instructions.
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.