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How the Math Works
Rails = Fence Sections × Rails per Panel
Pickets = [ (Post Spacing × 12) ÷ (Picket Width + Gap) ] × Fence Sections
Whether you are a DIY homeowner looking to build a privacy fence or a contractor bidding on a massive landscaping project, accurately estimating your materials is the most critical step. Over-ordering leaves you with expensive lumber rotting in your driveway, while under-ordering stalls the project and requires emergency trips to the hardware store.
Our free Fence Calculator takes the guesswork out of the building process. Simply input your fence dimensions and spacing preferences, and the tool will instantly output exactly how many posts, horizontal rails, pickets, and bags of concrete you need to complete the job.
How to Use the Fence Calculator
We designed this tool to handle everything from standard privacy fences to split-rail farm boundaries.
- Select a Preset (Optional): If you are building a standard fence, click one of the quick presets at the top to automatically fill in the standard width and spacing measurements.
- Enter Fence Length: Input the total linear feet of the area you intend to fence.
- Adjust Spacing: Standard posts are set 8 feet apart, but you can adjust this if you are building heavy-duty panels that require 6-foot spacing.
- Enter Gates: Every gate you add requires an extra post for structural framing.
- Estimate Cost (Optional): If you know the local hardware store prices for lumber, enter them in the bottom section to generate a total project cost!
The Fencing Formula
Calculating the materials by hand requires a few specific layout formulas. Here is exactly how the calculator determines your material list behind the scenes:
Total Fence Posts:
First, we divide your total fence length by the distance between posts to find the number of “sections.” We then add 1 (because a fence with 1 section still needs a post at the beginning and the end). Finally, we add 1 extra post for every gate you include.
- Formula: Total Posts = (Total Length ÷ Post Spacing) + 1 + Gates
Total Horizontal Rails:
The rails are the horizontal 2x4s that run between the posts. We take the total number of sections and multiply it by how many rails you want per panel.
- Formula: Total Rails = Fence Sections × Rails per Panel
Total Pickets:
To find the exact number of pickets (or slats), we convert the post spacing into inches. Then, we divide that number by the combined width of the picket and the gap space between them.
- Formula: Pickets per Section = (Post Spacing in inches) ÷ (Picket Width + Gap Space)
Fencing Types and Standard Spacing
If you are buying lumber for the first time, use this quick reference guide to understand standard building materials in the US:
| Fence Style | Standard Picket Width | Gap Between Pickets | Standard Rails Needed |
| Solid Privacy | 5.5 inches | 0 inches | 3 rails (top, middle, bottom) |
| Shadowbox | 5.5 inches | 3.5 inches | 3 rails |
| Standard Picket | 3.5 inches | 2 inches | 2 rails (top, bottom) |
| Split Rail | No Pickets | No Pickets | 2 or 3 rails |
Frequently Asked Questions (FAQs)
How far apart should my fence posts be?
The industry standard for residential wood fencing is 8 feet apart. However, if you are building an exceptionally tall fence (8+ feet), using incredibly heavy materials, or living in an area with extreme wind, contractors will often drop the spacing to 6 feet for added strength.
How many bags of concrete do I need per fence post?
A general rule of thumb is to use two 80-lb bags of concrete per post. The hole should be dug down to below your local frost line (usually 2 to 3 feet deep) and should be roughly three times wider than the post itself.
What is the actual width of a standard fence picket?
When you buy a standard “1×6” picket at the hardware store, it does not actually measure 6 inches wide. Due to the milling and drying process, the “actual” width of a 1×6 picket is exactly 5.5 inches. (Likewise, a 1×4 picket is actually 3.5 inches wide). Our calculator accounts for this by using 5.5 inches as the default standard width!
Should fence posts be set in concrete or dirt?
Wooden fence posts should almost always be set in concrete. Setting them directly in dirt or gravel drastically increases the chance of the post rotting from moisture or leaning over during a strong storm.
How many pickets do I need for a 100-foot privacy fence?
Assuming you use standard 5.5-inch pickets with zero spacing (no gaps), you will need roughly 219 pickets to complete 100 linear feet of fencing.