Stairs, decks and fences

Fence calculator: posts, rails, pickets and concrete

A wood fence is posts at a set spacing, two or three rails between each pair, and pickets along the whole run. Here is the count for 100 ft of fence, and the concrete to set the posts.

How many fence posts do I need?

Divide the length of the run by the post spacing, usually 8 ft at most for wood rails, and round up: that is the number of sections. There is one more post than sections. Gates and corners need their own posts.

Example. 100 ft at 8 ft spacing: 100 ÷ 8 = 12.5, so 13 sections and 14 posts. Spread evenly, the posts are 100 ÷ 13 = 7.69 ft apart, about 7 ft 8 5/16 in on center.

How many rails?

Each section takes two rails for a short fence and three for a taller one.

Example. 13 sections × 2 rails = 26 rails; with three rails, 39.

How many pickets?

Divide the run by the picket width plus the gap between pickets, then add a little waste, about 5 percent.

Example. 5 1/2 in pickets with a 1/2 in gap take 6 in each: 1,200 ÷ 6 = 200 pickets, or 210 with 5 percent waste.

How much concrete per fence post?

The concrete fills the hole around the post: the volume of the hole minus the part of the post in it, worked out like any concrete volume. Hole depth depends on the frost line and the fence height, so check your local rules.

Example. A 10 in round hole 30 in deep holds π × 5² × 30 = 2,356 cu in, or 1.36 cu ft. A 4x4 post (3 1/2 in square) takes 0.21 cu ft of that, leaving 1.15 cu ft: two 80 lb bags at about 0.6 cu ft each.

Fences in Clad

Clad's fence tool takes the length, the post spacing, the rails per section, the picket width, the gap and the waste, and gives the sections, posts, rails and pickets, with a cost when you add a price per picket. They go into the job's shopping list together.