What the calculator assumes
A wood fence built from loose parts. Posts are set in concrete. Rails run from post to post. Pickets are nailed to the rails side by side and run past the posts. The same math works for a tight privacy fence and for a picket fence with wide gaps. Only the picket width and the gap change.
Leave the gate openings out of the fence length. Each gate adds one post, so there is a post on both sides of the opening. The gate itself is not in the list.
How it works
- Sections = fence length ÷ post spacing, rounded up
- Posts = sections + 1, plus 1 more for each gate
- Rails = sections × rails per section
- Pickets = fence length ÷ (picket width + gap), rounded up
- Picket nails or screws = pickets × rails per section × 2
- Hole depth = post depth in the ground + gravel
- Concrete = 3.1416 × hole radius² × post depth × posts, then ÷ what one bag makes, rounded up
Example: 100 feet of 6 foot fence with one gate, posts no more than 8 feet apart, 5.5 inch pickets and a 1/8 inch gap. Sections = 100 ÷ 8 = 12.5, so 13. Posts = 13 + 1 + 1 for the gate = 15. Rails = 13 × 3 = 39. Pickets = 1,200 inches ÷ 5.625 = 213.3, so 214. Fasteners = 214 × 3 × 2 = 1,284. Each hole is 12 inches wide with 24 inches of concrete, which is 3.1416 × 0.5² × 2 = 1.57 cubic feet. Fifteen holes need 23.56 cubic feet. A 50 lb bag makes 0.375 cubic feet, so that is 63 bags.
The calculator spreads the posts evenly, so 100 feet in 13 sections puts them about 7 feet 8 inches apart. It does not take the post out of the hole volume. The post fills a little of the hole, and that small difference is your margin for spills and uneven holes.
Setting the posts
Quikrete's post setting guide says to dig the hole about 3 times as wide as the post, which is about 12 inches for a 4 inch post. It puts the depth at a third to a half of the post height above the ground, so at least 2 feet for a 6 foot fence, with about 6 inches of gravel in the bottom for drainage. Fence makers give similar numbers. Universal Forest Products says to put a third of the post length in the ground, dig holes 10 to 12 inches wide, and set end, corner and gate posts at least 6 inches deeper.
Where the ground freezes, dig below the frost line. Your building department can tell you that depth. For a 6 foot fence with posts 2 feet in the ground, an 8 foot post is long enough. Deeper holes need 10 foot posts. Let the concrete cure for 24 to 48 hours before you hang rails on the posts.
Rails and pickets
Universal Forest Products calls for two rails on shorter fences, three on a 6 foot fence and four on an 8 foot fence, with each rail set on edge so it does not sag. Sequoia Forest Products puts the top rail about 6 inches below the picket tops and the bottom rail about 6 inches above the ground, with the third rail centered between them. End each rail on the middle of a post.
For a privacy fence, set the pickets tight or use a 1/8 inch spacer so the wood has room to swell. For a picket fence, cut a scrap board to the gap you want and use it as a spacer. Keep the bottom of the pickets at least an inch off the ground so they do not soak up water. Each picket gets two nails or screws at every rail. Buy a few spare pickets, because some will split or come warped.
Before you dig
Call 811 before you dig to have buried lines marked. Fence height limits, setbacks and permits are local rules, so check with your city or county first. Make sure you know where the property line is, and tell the neighbors along it what you plan.
Common questions
How many fence posts do I need for 100 feet of fence?
With posts no more than 8 feet apart, 100 feet takes 13 sections and 14 posts. Add one post for each gate. At 6 foot spacing it takes 17 sections and 18 posts.
How far apart should fence posts be?
No more than 8 feet center to center for a wood fence built with 8 foot rails. Sequoia Forest Products recommends 6 feet for the strongest fence. Ready-made panels set their own spacing, so follow the panel instructions.
How deep should a fence post be in the ground?
Quikrete gives a third to a half of the height above the ground, so 2 to 3 feet for a 6 foot fence. Add about 6 inches for gravel under the post. Where the ground freezes, go below the frost line.
How many pickets do I need per foot of fence?
About 2.1 per foot with 5.5 inch pickets and a 1/8 inch gap. That is 214 pickets for 100 feet. With 3.5 inch pickets and a 2.5 inch gap it is 2 per foot.
How many bags of concrete do I need per fence post?
A hole 12 inches wide with 24 inches of concrete holds 1.57 cubic feet. That is about 4.2 bags of 50 lb mix, or 2.6 bags of 80 lb mix, for each post. Yields are for standard concrete mix, so check the bag if you use a fast-setting mix.
How many rails does a 6 foot fence need?
Three. Fence makers call for two rails on shorter fences, three at 6 feet and four at 8 feet. The extra rail keeps tall pickets from warping.
Tools for this job
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- Long tape measure. Measures the fence line and marks the post spacing.
- Mason line. Stretches between the end posts to keep the fence straight.
- Marking paint. Marks each post spot on the ground.
- Post hole digger. Digs a narrow hole for each post.
- Digging bar. Breaks up rocks and hard soil, and packs the fill around each post.
- Post level. Straps to a post and shows plumb on two sides at once.
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Sources
- Quikrete, Setting Posts in Concrete (hole width, depth and gravel)
- Universal Forest Products, Wood Fence Kits installation instructions
- Sequoia Forest Products, Building a 6-Foot Redwood Privacy Fence
- Quikrete Concrete Mix data sheet (yield per bag)
Facts on this page were last checked against these sources in October 2026.