What is on-center post spacing?

On-center (OC) spacing is the distance measured from the center of one post to the center of the next. Common values are 6 ft and 8 ft. Shorter spacing gives more support but uses more posts.

How many rails does a typical fence need?

A fence under 4 ft tall usually needs 2 rails; 4–6 ft fences typically use 3 rails; taller privacy fences may use 4 rails. More rails add rigidity.

Why add a waste percentage?

Lumber comes in fixed lengths and cuts may not divide evenly. A 5–10% waste buffer accounts for offcuts, damaged boards, and measuring errors.

Does the calculator include corner and gate posts?

The calculator computes line posts based on bay count. Add 2 posts for each corner and 2–3 posts per gate opening on top of the calculated total.

What gap should I leave between pickets?

Privacy fences typically have 0 gap; decorative picket fences leave 1.5–3 inches between boards. Enter picket width plus desired gap as the "picket width" to space them automatically.

How do I calculate total fence cost?

Multiply each material count by your local lumber price per unit. Add concrete (typically 1–2 bags per post hole), hardware, and labor for a complete budget.

Fence Calculator

Name: Fence Calculator
Availability: InStock
Author: Nham Vu

Enter your fence length, post spacing, rail count, and picket width to instantly calculate how many posts, rails, and pickets you need.

Fence Parameters

Total Fence Length (ft)

Post Spacing — On Center (ft)

Common: 6 ft or 8 ft between post centers.

Rails per Bay

Picket / Board Width (inches)

Include gap in this value for spaced pickets. Standard 1×4 = 3.5 in.

Waste Buffer (%)

Fill in your fence details and click Calculate to see your materials list.

Summary

Enter your fence length, post spacing, rail count, and picket width to instantly calculate how many posts, rails, and pickets you need.

How it works

Enter the total length of the fence run in feet.
Set the on-center post spacing (typically 6 or 8 feet).
Choose how many horizontal rails span each bay (usually 2 or 3).
Enter the width of each picket or board in inches.
Optionally add a waste percentage (5–10% is standard).
The calculator returns post count, rail count, and picket count — ready for your shopping list.

Use cases

Planning a wood privacy fence around a backyard.
Estimating picket quantities for a decorative front yard fence.
Calculating rail lumber for a split-rail or ranch-style fence.
Comparing material costs for different post spacing options.
Building a temporary construction site barrier.
Replacing or repairing a section of an existing fence.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu