Fence Calculator
Calculate posts, pickets, rails, and concrete for your fence project.
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How to Calculate Fence Materials
Planning a fence project starts with accurate material estimates. Under-ordering means a second trip to the hardware store mid-project; over-ordering wastes money. This fence calculator breaks down every component — posts, pickets, rails, and concrete — so you know exactly what to buy.
Posts
Posts are the structural backbone of your fence. Divide total fence length by post spacing and round up to get the number of sections (bays), then add one post for the end of the run: 100 ft ÷ 8 ft = 12.5, rounded up to 13 sections, so 14 posts. For a closed loop, skip the +1. Each corner that does not fall exactly on your spacing needs roughly one extra post, and each gate needs its own hinge and latch posts set to the gate width rather than the panel spacing.
Post length = fence height + the buried depth, which should be at least one third of the total post length. For a 6-ft fence, use 9-ft posts buried 3 ft deep. Use 4×4 posts for fences up to 6 feet and 6×6 posts for 8-foot fences, windy sites, and double-gate posts.
Pickets
Calculate pickets per linear foot: 12 ÷ (picket width + gap). For 3.5-inch pickets with 0.5-inch gaps: 12 ÷ 4 = 3 pickets per foot. For 100 linear feet: 300 pickets. A full-privacy fence with no gap uses 12 ÷ 3.5 ≈ 3.4 pickets per foot, but boards shrink as they dry, so a butted fence often opens small gaps within a season. Add 10% waste for cuts and defects: 330 pickets. Standard picket length = fence height + ~3 inches to account for setting height above grade.
Rails
Rails per bay depend on height: 2 rails for fences up to 4 feet, 3 rails (top, middle, bottom) for 5–6 foot fences, and 4 rails for 7–8 foot fences. Total rails = rails per bay × number of bays. Rails are 2×4 lumber cut to span post to post, which is why 8-foot spacing is so common: an 8-foot board needs no cutting. Buy 2–3 extra for end cuts and warped pieces.
Concrete
The calculator treats each post hole as a cylinder and subtracts the volume of the post itself. A 10-inch hole 36 inches deep holds 1.64 cubic feet; a 4×4 post takes up 0.26 of that, leaving about 1.38 cubic feet of concrete, or 2.3 bags of 80-lb mix (each yields about 0.6 cubic feet). A good rule for hole diameter is about three times the post width: 10–12 inches for a 4×4, 16 inches or more for a 6×6. Gate and corner posts carry more load, so go wider and deeper there. If you put 4–6 inches of gravel in the bottom of each hole for drainage, reduce the hole depth you enter by the same amount.
Setting Posts
Set the end and corner posts first, then run a string line between them to align the line posts. Plumb each post on two adjacent faces and brace it with scrap 2×4s. Fast-setting mix can be poured dry around the post and watered in place; regular mix is stronger but needs mixing in a wheelbarrow. Crown the top of the concrete so it slopes away from the post and sheds water, and let posts cure 24–48 hours before hanging rails.
Gate Openings
Walk gates are usually 3–4 feet wide; driveway double gates run 8–12 feet. Gate posts take far more sideways force than line posts, so use 4×4s for a single walk gate and 6×6s for double gates, set deeper and in larger holes. Use heavy-duty galvanized hinges, and add an anti-sag cable and turnbuckle kit on any gate wider than about 4 feet, since every wood gate sags over time.
Hardware and Extras
Don't forget: galvanized or stainless screws or nails (about 1 lb per 50 linear feet), post caps to prevent water damage, gate hardware if applicable, and stain or sealer for long-term protection. Cedar and redwood naturally resist rot; pressure-treated pine needs sealer to prevent checking and graying.
Frequently Asked Questions
With 8-ft post spacing: 100 ÷ 8 = 12.5, which rounds up to 13 sections, plus 1 for the final post = 14 posts. With 6-ft spacing: 17 sections + 1 = 18 posts. For a closed perimeter that ends where it started, skip the +1, because the last post is the first one. Add roughly one extra post for each corner that does not land on your spacing.
8 feet on center is standard for wood privacy fences, because 8-ft rails and panels span it with no waste. Chain-link and vinyl fences typically use 6 feet, and split-rail fences 10–12 feet. On hillsides or in windy spots, 6-foot spacing gives a stiffer fence that follows the terrain better, at the cost of more posts.
At least one third of the total post length: 9-ft posts buried 3 ft deep for a 6-ft fence. In cold climates the bottom of the hole must sit below the local frost line, often 36–48 inches, or frost heave will push posts up and the fence will lean. A 10-inch hole 36 inches deep around a 4×4 takes about 1.4 cubic feet of concrete, a little over two 80-lb bags.
It depends on picket width and gap. 3.5-inch pickets with 0.5-inch gaps: about 300 per 100 feet. 5.5-inch pickets with 0.5-inch gaps: about 200. For a zero-gap privacy fence with 3.5-inch pickets, 12 ÷ 3.5 ≈ 3.4 per foot, or about 343 per 100 feet. Add 10% for cuts and defects.
Pressure-treated pine is the most affordable and widely available; use ground-contact rated posts and treat cut ends with end-grain preservative. Cedar and redwood resist rot naturally and look better but cost 50–100% more. Use 4×4 posts for fences up to 6 feet and 6×6 posts for 8-foot fences, windy sites, and double gates. Vinyl and chain-link fences use steel or aluminum posts instead.
Many municipalities require permits for fences over a certain height (often 6 feet). Check your local building department, HOA rules, and property survey to verify setback requirements before starting, and call 811 to have buried utilities marked before you dig post holes. Fence placement errors can be expensive to correct.