Fence Calculator
One run length in — posts, sections, pickets, rails and the concrete to set it all, shopping-list style.
The short answer
Formula. Posts = run length ÷ post spacing + 1; pickets = run × 12 ÷ (picket width + gap), rounded up; rails = sections × rails per section.
Example. A 100-ft privacy run at 8-ft post spacing needs 14 posts and 219 pickets from 5.5-in boards butted tight.
How this calculator works
Posts first, because everything hangs on them. Divide your run length by the post spacing and round up for sections, then add one for the closing post: a 100 ft run at 8 ft on center is 13 sections and 14 posts (the last section runs short, or you stretch spacing a hair — real fence lines are never exactly divisible). Sections × rails-per-section give rail boards cut to the spacing; if you buy 16-ft 2×4s, each covers two 8-ft sections, so divide by two — 26 rails becomes 13 boards.
Pickets are pure division: the run length in inches divided by picket width plus gap, rounded up. A 100 ft privacy run with 5.5 in pickets butted tight is 1,200 ÷ 5.5 ≈ 219 pickets; open the spacing to 1 inch and it drops to ~185, which is exactly why spaced-picket fences cost less per foot. Add 3–5% for warped tops and splitting at nail points — buy by the bundle and returns are painless.
Concrete closes the shopping list, and the calculator does it honestly: each hole is a cylinder (π × radius² × depth) minus the buried post volume, summed across posts and divided by your bag's yield — 0.375 cu ft for 50 lb fast-setting mix, straight off the bag. A 4×4 in a 10-inch hole 24 inches deep needs about 0.92 cu ft, and a 14-post run about 12.9 cu ft = 35 bags. Two shortcuts pros use: gate posts get a wider hole and extra bag each (gates are levers), and tamped gravel alone can set fence posts in dry, well-draining soil — concrete is for clay, frost and gates.
Sources & review date
- Post spacing of 6–8 ft and 2–3 rails per section are standard fence-building practice; check local bylaws for height limits and property-line setbacks.
Last reviewed: October 2026. Numbers that drift (fees, prices, densities) are editable inputs on this page.
Fence FAQs
How much does a 100 ft privacy fence cost in materials?
Ballpark with the shopping list above: 14 posts, 13 rail boards, ~219 pickets, ~35 bags of concrete and a box of hanger brackets/nails. Prices swing by region and wood species — run your local prices against the counts this page gives you.
Should fence posts be set in concrete or gravel?
Concrete for gate posts, clay soils, frost heave zones and heavy privacy fences; compacted gravel works well for line posts in sandy, fast-draining soil and lets water drain away from the post foot. Both methods want the hole wider than deep-thinking suggests: diameter matters more than depth beyond the frost line.
How deep should fence posts go?
Rule of thumb: one third to one half of the above-ground height, and at least to your local frost line (48 in in cold climates). The calculator default, 24 in, suits a 4–5 ft fence in mild-winter areas — change it to your conditions.
Do I need a permit to build a fence?
Often yes, and usually with height limits and "finished side out" rules set by your municipality. Check before digging, and call the utility locate service before any hole — both are free-to-cheap and fines are not.