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Fence Calculator: Plan Your Perimeter Like a Pro

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Fence Calculator: Plan Your Perimeter Like a Pro

Good fences make good neighbors, but bad calculations make for expensive weekends. If you order too few pickets, you leave a gap in your privacy.

If you dig your post holes too shallow, the wind will knock your investment over in a year. Use this engineering-grade tool by ShockTrail to generate a precise material list for Wood, Vinyl, or Chain Link projects.

The Material Estimator

Enter your total fence length to calculate Posts, Rails, Pickets, and Concrete.

Fence Estimator

Posts • Pickets • Concrete

Total Fence Length (ft)

Number of Gates Adds extra posts

Fence Style

Height (Rails)

Structural Materials

4x4 Posts (Pressure Treated) 0

Concrete Bags (50lb) 0

2x4 Rails (8ft long) 0

Infill Materials

Pickets Needed 0

Fasteners (Screws/Nails) 0 lbs

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PART 1: The Geometry of a Fence

A fence is a system of three components that must work together structurally:

Posts: The anchors. Usually 4×4 or 4×6 pressure-treated timber set in concrete.
Rails (Stringers): The horizontal 2x4s that connect the posts. A 6-foot fence needs 3 rails; a 4-foot fence needs 2.
Infill (Pickets/Panels): The visible part.

The “8-Foot Rule” vs. Reality

Lumber is sold in 8-foot lengths. Therefore, standard post spacing is 8 feet on center. However, if you dig your holes exactly 8 feet apart, you leave zero room for error. Most pros dig holes at 7′ 10″ spacing. This allows you to trim the rails for a perfect fit rather than coming up 1 inch short.

PART 2: Real-World Case Studies

Material lists change drastically based on style. Let’s analyze three common builds.

Case Study 1: The Dog-Ear Privacy Fence (Wood)

The Project: A standard 6ft tall privacy fence for a backyard. Total length: 150 feet.

The Math:

Posts (8ft Spacing): 150 ÷ 8 = 18.75. Round up to 19 sections. Add 1 end post = 20 Posts.
Rails (3 per section): 19 sections × 3 rails = 57 2x4s (8ft long).
Pickets: Standard dog-ear pickets are 5.5″ wide. We assume no gap (privacy).150 ft × 12 = 1,800 inches.1,800 ÷ 5.5 = 327 pickets. Add 5% waste = 345 Pickets.
Concrete: 20 posts × 1.5 bags = 30 Bags.

Case Study 2: The Vinyl Panel Fence (Prefab)

The Project: Installing white Vinyl (PVC) panels. Total length: 100 feet.

The Math:

Vinyl is sold in pre-made 8-foot panels. You cannot change the width easily.
100 ÷ 8 = 12.5 Panels. You must buy 13 Panels and cut the last one.
Posts: 13 Panels require 14 Posts.
Important: Vinyl posts are hollow. You must install a treated wood 4×4 inside the gate posts for strength, or the swinging gate will warp the vinyl.

Case Study 3: The Shadowbox “Good Neighbor” Fence

The Project: A style where pickets alternate on both sides of the rail, allowing wind to pass through and looking good from both sides. Length: 80 feet.

The Math:

Posts: 80 ÷ 8 = 10 sections + 1 = 11 Posts.
Pickets: This style requires roughly 50% more pickets than a standard privacy fence because you are covering both sides with spacing.
Standard count: ~175. Shadowbox count: ~260 pickets.

PART 3: Setting Posts (Concrete & Depth)

The most physically demanding part of fencing is the digging. [Image of fence post hole diagram]

The Frost Line Rule

If you live in an area that freezes, you must dig your post holes below the frost line (typically 30 to 48 inches deep). If you don’t, the frozen ground will heave (expand) and push your post out of the ground, ruining your straight fence line.

Concrete Calculation

For a standard 4×4 post in a 10-inch diameter hole:

No-Mix Method: Pour dry concrete into the hole and add water. Fast but weaker. Requires ~2 bags (50lb).
Pre-Mix Method: Mix in a wheelbarrow. Stronger. Requires ~1.5 bags (50lb).

PART 4: Wood Expansion (The Gap)

If you use Pressure Treated Pine pickets straight from the store, they are soaking wet (heavy with chemical treatment).

Do NOT leave a gap. Butt them tightly together. When the sun dries them out over 4 weeks, they will shrink by about 1/4 inch, creating the perfect gap naturally.

If you use Cedar or Kiln-Dried wood, you must manually space them (use a nail as a spacer) because they will not shrink much.

PART 5: Gates (The Weak Link)

A gate puts massive leverage on the hinge post. Over time, gravity pulls it down (sagging).

ShockTrail Recommendation:

Use 6×6 posts for gates instead of 4x4s.
Dig the gate post holes deeper (36″+).
Use a diagonal cross-brace on the gate frame (running from the bottom hinge up to the top latch) to transfer the weight back to the post.

Frequently Asked Questions (FAQ)

How many rails do I need?

For a 4-foot fence, 2 rails are standard. For a 6-foot fence, use 3 rails (top, middle, bottom) to prevent the pickets from warping.

Should I set posts in concrete or gravel?

Concrete is stronger but traps water, rotting the post faster. Gravel drains well but is less stable. Best Method: Put 3 inches of gravel at the bottom of the hole for drainage, then pour concrete around the post.

Do I need a survey?

Yes. Never guess your property line. If you build 6 inches onto your neighbor’s land, they can legally force you to tear it down. Rent a metal detector to find your property pins.