Why does a gate add a post rather than save one?

Because the opening still needs framing. A gate removes fence but needs a post on each side, one to hang from and one to latch to. In the middle of a run that is a net gain of one post compared with the same run with no gate in it.

How deep should posts go?

The common rule of thumb is about a third of the fence height, with 24 inches as a floor. But the depth that actually governs is your local frost line and your local code, and both can require considerably deeper. This is one of the few things worth a phone call before you start.

Do corner posts need to be bigger?

They carry more load than line posts, being pulled in two directions rather than one. Many builders use a 6×6 at corners and gates, or set them deeper, or both. The count here separates them so you can order accordingly.

Can I reuse the existing post holes?

Rarely worth it. Old holes are usually the wrong size, often full of the previous concrete, and almost never in the right place once you have picked your own spacing. Most rebuilds dig fresh.

Fence Ledger

Fence Post Calculator

How many posts your fence needs — counted properly, including the ones corners and gates force on you.

Units

Shape

Fence length

Height

Gates

Post spacing

Advanced options

These are typical values, not requirements. Post depth in particular is governed by your local frost line and building code — check before you dig.

Gate width

Picket gap

Hole diameter

Hole depth

Gravel base

Bag yield

Waste allowance

Posts

Sections

Pickets

336

Concrete

35 bags

Estimated cost

Materials only (DIY)

$1,400 – $3,600

Professionally installed

$3,950 – $8,850

National planning ranges compiled from published US construction cost guides, last checked September 2026 (confidence: medium-low). Prices vary sharply by region, season and contractor. These are estimates for planning, not quotes.

Sources: homeguide.com, calcsummit.com, angi.com, ergeon.com, homewyse.com

Shopping list

Bill of materials for this fence
Material	Size	Quantity
Posts	4x4	21
Rails incl. waste	2x4	63
Pickets incl. waste	1x6	336
Concrete mix		35bags
Gravel		8bags
Exterior screws		≈2,200
Walk gate kit		1

Why these numbers

How we got the section count

Run 1: 146 ft ÷ 8 ft = 18.25, rounded up to 19 sections

How we got the post count

3 posts are fixed by the shape itself
2 at the open ends
1 carrying a gate
18 line posts spaced between them
21 posts in total

How we got the picket count

Each picket covers 5.5 in plus a 0.25 in gap, so they repeat every 5.75 in
146 ft of fence needs 305 pickets
Plus 10% for offcuts, rounded up to 336

How we got the concrete

Each 10 in hole is 30 in deep, less 4 in of gravel base, leaving 26 in of concrete
The 4x4 post itself takes up part of that, so each hole needs the remainder
Across 21 posts
Divided by the 0.6 cu ft a bag yields: 34.91, so buy 35 bags

The formula everyone uses is wrong

Divide the length by the spacing, round up, add one. That is correct for a single unbroken straight run and undercounts every other shape, because it treats the fence as one continuous thing when it is not.

Some posts are not optional. Every corner needs one, because you cannot span a change of direction with a rail. Every gate needs one on each side. Every open end needs one. Those forced posts cut the fence into independent runs, and each run has to be divided and rounded on its own.

What that difference looks like

On a 50 by 30 foot yard, rounding each side separately gives 22 posts. Rounding the 160-foot perimeter as a whole gives 20. Two posts is not much money, but it is a second trip, and you find out about it with the holes already dug.

On an L-shaped run of 75 and 42 feet, the gap is one post and one section of rail. The pattern holds for every shape with a corner in it: the more corners, the more the shortcut costs you.

Spacing, and why eight feet

Eight-foot centres are the residential default for one practical reason: 2×4 rail stock is commonly sold in eight-foot lengths, so one rail spans exactly one section from post centre to post centre with nothing to cut and nothing to join.

Closer spacing costs more posts and more concrete but sags less, which matters on tall fences and exposed sites. Wider spacing means cutting and joining rails mid-span, which is weaker and wastes material. Both are available here; eight is where most projects land.

Common questions

Why does a gate add a post rather than save one?: Because the opening still needs framing. A gate removes fence but needs a post on each side, one to hang from and one to latch to. In the middle of a run that is a net gain of one post compared with the same run with no gate in it.
How deep should posts go?: The common rule of thumb is about a third of the fence height, with 24 inches as a floor. But the depth that actually governs is your local frost line and your local code, and both can require considerably deeper. This is one of the few things worth a phone call before you start.
Do corner posts need to be bigger?: They carry more load than line posts, being pulled in two directions rather than one. Many builders use a 6×6 at corners and gates, or set them deeper, or both. The count here separates them so you can order accordingly.
Can I reuse the existing post holes?: Rarely worth it. Old holes are usually the wrong size, often full of the previous concrete, and almost never in the right place once you have picked your own spacing. Most rebuilds dig fresh.