Are 2x4s the only option for rails?

They are the common one for residential wood fence. Heavier stock appears on taller fences and on exposed sites, and some builders use a wider board laid flat as a top rail for stiffness. What matters is that the rail can span the post spacing without sagging.

Do rails need to be pressure treated?

They are less exposed than the posts, which sit in the ground, but they still get wet and stay wet where the pickets touch them. Most people use treated stock throughout for a fence expected to last, and it is a small share of the total cost.

How are rails fixed to the posts?

Either butted between the posts on brackets or cleats, or run across the face of the posts and fixed through. Face-fixing is faster and stronger in tension; butting looks tidier and keeps the fence line flat. Both need enough fasteners at each joint, which the calculator estimates.

Fence Ledger

How many 2x4s do I need for a 100 ft fence?

Rail stock is the item people most often underbuy, because it is easy to work out from the fence length and easy to get wrong by one whole multiple.

Rails needed

3 per section across 13 sections, plus a 10% waste allowance.

What the usual answer misses

The trap is multiplying the fence length by the rails per section instead of multiplying the section count by it. Those are different numbers whenever the run does not divide evenly by the post spacing, and they diverge further the more corners and gates the fence has, because each forced post adds a section boundary. Count sections first, then rails.

Work out your own

Every assumption above is editable. Change the length, the spacing, the hole size — the numbers and the working update as you go.

Units

Shape

Fence length

Height

Gates

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.

Post spacing

Gate width

Picket gap

Hole diameter

Hole depth

Gravel base

Bag yield

Waste allowance

Posts

Sections

Pickets

222

Concrete

24 bags

Estimated cost

Materials only (DIY)

$1,000 – $2,600

Professionally installed

$2,700 – $6,100

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	14
Rails incl. waste	2x4	40
Pickets incl. waste	1x6	222
Concrete mix		24bags
Gravel		6bags
Exterior screws		≈1,500
Walk gate kit		1

Why these numbers

How we got the section count

Run 1: 96 ft ÷ 8 ft = 12, rounded up to 12 sections

How we got the post count

3 posts are fixed by the shape itself
2 at the open ends
1 carrying a gate
11 line posts spaced between them
14 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
96 ft of fence needs 201 pickets
Plus 10% for offcuts, rounded up to 222

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 14 posts
Divided by the 0.6 cu ft a bag yields: 23.27, so buy 24 bags

Common questions

Are 2x4s the only option for rails?: They are the common one for residential wood fence. Heavier stock appears on taller fences and on exposed sites, and some builders use a wider board laid flat as a top rail for stiffness. What matters is that the rail can span the post spacing without sagging.
Do rails need to be pressure treated?: They are less exposed than the posts, which sit in the ground, but they still get wet and stay wet where the pickets touch them. Most people use treated stock throughout for a fence expected to last, and it is a small share of the total cost.
How are rails fixed to the posts?: Either butted between the posts on brackets or cleats, or run across the face of the posts and fixed through. Face-fixing is faster and stronger in tension; butting looks tidier and keeps the fence line flat. Both need enough fasteners at each joint, which the calculator estimates.