Fence Measurements
Fence Style & Pickets
Gates
Concrete Mix
Total Pickets Needed
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Enter your fence length above to get started
Total Posts
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line + terminal
Horizontal Rails
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-- per section
Concrete Bags (50lb)
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-- bags per post
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Key Terms Explained
Terminal Post
A post at any end, corner, or gate opening that bears load from only one direction. Set deeper and in more concrete than line posts.
Line Post
Any post in the middle of a straight fence run. Supports rails on both sides and keeps panel spacing consistent.
Picket
An individual vertical board nailed to the horizontal rails. Picket width and gap determine how many you need per linear foot of fence.
Rail
A horizontal board that runs between posts and supports the pickets. Most fence styles use 2 or 3 rails per panel section.
Plumb
Perfectly vertical, as verified with a level. Posts must be plumb before concrete sets or the entire fence run will lean.
Frost Line
The maximum depth that groundwater in soil can freeze during winter. Posts must be set below the local frost line to prevent heaving.
Setback
The required minimum distance between a fence and a property line, easement, or structure, as defined by local zoning ordinances.
On-Center (O.C.)
A measurement taken from the center of one structural member to the center of the next. Standard fence post spacing is specified O.C.
The Complete Guide to Estimating Fence Materials
Whether you're building a 6-foot cedar privacy fence around your backyard or a spaced-picket boundary fence along your property line, running out of posts mid-dig or coming up short on pickets is a frustrating and expensive mistake. This estimator handles the math so you can walk into the lumber yard with a confident, itemized list.
How to Use This Tool
Start by entering your total fence length - the sum of all straight runs you plan to build. Choose feet or meters depending on how you measured. Select your post spacing (6 ft is standard for privacy fences; 8 ft is common for economy builds and farm fencing) and pick your fence style. If you have gates, add them: each single gate adds one terminal post, and each double gate adds two. Adjust the concrete slider to match your post hole specs. All outputs update in real time as you change any value.
Understanding the Post Count
Post count is calculated by dividing your total fence length by the on-center post spacing, then adding 1 for the final end post. A 100-foot run at 6-foot spacing requires 17 posts (100 / 6 = 16.67, rounded up to 17 sections, plus 1 end post = 18... or more precisely: Math.ceil(100/6) + 1 = 18 posts). This calculation gives you all your line posts plus the two terminal end posts. Additional terminal posts are added for gates on top of that baseline.
Rails and Pickets: Where the Cost Is
For a typical 6-foot privacy fence, 3 horizontal rails per section is standard - one near the top, one near the bottom, and one in the middle to prevent bowing over a long span. A 4-foot fence can get away with 2 rails. The total rail count is sections x rails per panel, where sections equals the number of spans between posts (one fewer than the post count on a straight run). Pickets are calculated by dividing the total fence length in inches by the effective picket width (board width plus any gap). A tight privacy fence using 1x6 boards at 5.5 inches each on a 100-foot run needs 218 pickets (1200 / 5.5 = 218.18, rounded up). Add even a 0.25-inch gap and the count drops to 207 - a meaningful difference when pricing lumber.
Concrete: Don't Shortchange the Foundation
A fence post set in loose or inadequately anchored concrete will lean within a season or two. The 1.5 bags default in this tool is appropriate for a standard 4x4 post in a 10-inch diameter hole set 2 feet deep. For 6x6 posts, posts set 3 feet deep, or gate and corner terminal posts that take heavy lateral loads, bump the slider to 2 or 2.5 bags. Always wet the concrete in the hole slowly and allow it to cure at least 24 to 48 hours before attaching rails and pickets.
Frequently Asked Questions
How deep should I bury my fence posts?
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The general rule is to bury one-third of the post's total length underground. For a 6-foot privacy fence using 8-foot posts, that means burying approximately 2 feet. In regions with a deep frost line, posts must extend below the frost depth to prevent heaving - in northern climates this can be 36 to 48 inches. Always check your local frost line depth before digging. Posts set in concrete should have the concrete collar slope away from the post at the top to shed water and prevent rot at the base.
What is the difference between a terminal post and a line post?
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A line post is any post in the middle of a straight fence run - it supports rails on both sides and keeps the fence panels spaced correctly. A terminal post is any post at the end of a run where only one side bears load: corner posts, end posts, and gate posts are all terminal posts. Terminal posts must be set deeper and set in more concrete because they bear the full tension of the fence pulling in one direction. Gate posts in particular take repeated lateral stress every time the gate swings, so they are often set in 3 to 4 bags of concrete versus the standard 1.5 to 2 bags for a line post.
How many bags of concrete do I need per fence post?
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The standard industry heuristic is 1.5 to 2 bags of 50lb concrete mix per fence post hole. A standard 4x4 post set 2 feet deep in a 10-inch diameter hole takes roughly 0.13 cubic feet of concrete, which is just under one 50lb bag. However, most contractors use 1.5 to 2 bags to account for the full hole depth, irregular soil, and to ensure the post base is fully encased. For 6x6 posts, gate posts, or corner posts set 3 feet deep, 2.5 to 3 bags is more appropriate. This estimator defaults to 1.5 bags per post and lets you adjust via the slider.
Do I need to leave a gap between privacy fence pickets for expansion?
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For a true solid privacy fence using pressure-treated pine, cedar, or redwood pickets, a small gap of 1/8 to 1/4 inch is often recommended between boards to allow for seasonal wood expansion. Kiln-dried lumber installed tightly butted together can cup or warp as it absorbs moisture, causing boards to bow outward. However, many contractors install pressure-treated pickets tight and let them dry in place - the slight shrinkage as the wood dries opens a natural gap. If you are installing composite or PVC pickets, follow the manufacturer's spacing recommendation, which is typically 1/8 inch. This estimator lets you set any gap size, including 0 for a fully tight install.
What does on-center post spacing mean for fence building?
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On-center (O.C.) means the distance is measured from the center of one post to the center of the next post, not from edge to edge. A 6-foot on-center spacing with 4x4 posts (3.5 inches wide) leaves approximately 5 feet 8.5 inches of open span between post faces. On-center measurement is the standard in fence building because it makes math consistent regardless of post thickness - your rail lengths and picket counts stay the same whether you use 4x4 or 6x6 posts. Always confirm whether your fence panels or pre-built sections are dimensioned on-center or face-to-face before ordering materials.
Estimates only. Material quantities are based on standard industry formulas and may vary depending on site conditions, post hole diameter, fence height, and lumber availability. Always add a waste factor of 5 to 10 percent when placing your lumber order. Consult local building codes for required post depth, setback distances, and permit requirements before beginning construction.