Posts, rails, and pickets from perimeter length
Enter your total fence run and post spacing, and this calculator estimates posts, rails, and pickets. Posts are spaced evenly (8 ft is standard), rails run horizontally between posts (2 rails for fences under 5 ft, 3 for taller), and pickets are counted across the run including gaps. It also tells you how many 80lb bags of concrete you'll need to set the posts — two bags per standard 4×4 post hole is the norm.
A 150 ft privacy fence with 8 ft post spacing: posts = ceil(150 ÷ 8) + 1 = 20 posts. Sections = 19, so 2 rails per section = 38 rails (16 ft 2×4s ripped in half gives 76 8-ft rails — or buy 19 16-ft 2×4s and cut each into two 8 ft rails). Pickets at 5.5" wide with no gap: 150 ÷ (5.5/12) = 327 pickets. Concrete: 40 bags of 80lb quikrete.
How deep should fence posts be? Bury 1/3 to 1/2 of the above-ground height, minimum 24". A 6 ft fence typically needs 36" holes — below the frost line in cold climates.
Should I use concrete for every post? For privacy and picket fences, yes. For long agricultural runs, corner and gate posts get concrete, line posts can be tamped dirt.
How many pickets for 100 ft of fence? With 5.5" pickets and 1/2" gaps: 100 ÷ (6/12) = 200 pickets.
Gate posts? Use heavier posts (6×6 for wide gates) and set them deeper with extra concrete — gates put leverage loads on posts.