Fence Post Size and Spacing: Chart for Wood and T-Posts

Most wood fences use 4 × 4 posts (3½ in square) set 6 to 8 ft apart, centre to centre; 6 × 6 posts are for taller or heavier fences and wide gates. A post goes into the ground by about a third to a half of its height above ground, so a 6 ft fence needs 8 ft posts. Wire fences use steel T-posts 8 to 12 ft apart: a 100 ft straight run at 10 ft spacing takes 9 T-posts between two braced wooden end posts.

Posts = sections + 1 for each straight run, plus 1 for each gate.

Fence post sizes

4 × 4 (about 3½ × 3½ in, or 100 × 100 mm in metric): Angi says these suit most residential fences. Gates of 3 to 6 ft can hang on 4 × 4 posts.
6 × 6 (about 5½ × 5½ in): extra strength for taller or heavier fences; Angi says 10 ft gates need them. Corner and gate posts are often a size up from the line posts.
Steel T-posts: for wire, mesh and livestock fencing, driven into the ground rather than set in concrete.

How far apart should fence posts be?

Space wood fence posts 6 to 8 ft apart, and never more than 8 ft: 8 ft suits most privacy and picket fences, and 6 ft gives a stiffer fence in windy places or with heavy boards. Metal T-posts for wire fencing usually go 8 to 12 ft apart.

Home Depot's privacy fence guide says posts should be no more than 8 ft apart and recommends 6 ft for the most strength; Angi gives 6 to 8 ft for most fences. Closer posts cost more but make a stiffer fence in wind.

Posts for one straight run, by spacing
Post spacing	100 ft fence	200 ft fence	330 ft fence
6 ft	18	35	56
8 ft	14	26	43
10 ft	11	21	34
12 ft	10	18	29

Each run has one more post than sections. Add one post for every extra straight run (each corner) and every gate.

T-posts per 100 feet

Tractor Supply recommends T-posts 8 to 12 ft apart, with 10 to 12 ft enough for a five- or six-strand barbed wire fence, driven 18 to 24 in deep so the anchor plate is buried. Corners and gates take wooden posts set in concrete and braced, because that's where the wire pulls hardest. Red Brand, a fence wire maker, also gives 8 to 12 ft for most fences.

For 100 ft between two wooden end posts: 12 T-posts at 8 ft, 9 at 10 ft or 8 at 12 ft.

How deep should fence posts be?

Quikrete's guidance is a depth of one-third to one-half of the post's height above ground, a hole about three times the post's width, and about 6 in of gravel in the bottom for drainage. Home Depot's guide says at least 24 in. Dig below the frost line where you live, which can be deeper.

Hole depth and post length by fence height
Fence height	Post depth (⅓–½ of height)	Post length to buy
3 ft	12–18 in	6 ft
4 ft	16–24 in	6 ft
5 ft	20–30 in	8 ft
6 ft	24–36 in	8 ft
8 ft	32–48 in	12 ft

Post lengths are the shortest common length that gives the minimum depth; for the deeper end of the range, buy the next length up. Our post hole concrete calculator works out the concrete for any hole.

Picket spacing

Picket gaps are mostly a matter of looks. Pool fences are the exception: the US Consumer Product Safety Commission's guidelines say openings in a pool barrier shouldn't let a 4 in sphere pass, and the barrier should be at least 48 in high. Local codes can be stricter, so check before you build.

Pickets for 100 ft of fence
Picket width	Gap	Pickets
3.5 in	None (privacy)	343
3.5 in	1.5 in	240
3.5 in	2.5 in	200
5.5 in	None (privacy)	219
5.5 in	0.5 in	200

Worked example: 100 ft of picket fence

8 ft sections: 100 ÷ 8 = 12.5, so 13 sections and 14 posts.
Two rails per section: 26 rails.
3½ in pickets with 2½ in gaps take 6 in each: 1,200 in ÷ 6 = 200 pickets.
Concrete for 14 posts in 10 in holes, 30 in deep with 6 in of gravel: 24 bags of 80 lb mix.

The fence calculator does panels or pickets, gates and several runs; for a chart of posts by fence length, see how many fence posts you need.

Common mistakes

Spacing wider than the rails allow. Rails sold in 8 ft lengths need posts at 8 ft or less, measured centre to centre.
Light gate posts. Gates pull on their posts every time they swing. Use a heavier post set deeper.
T-posts at corners. Wire tension pulls corner T-posts over. Use braced wooden posts there.