Fence Material Calculator

Count posts, rails, pickets and concrete bags for a run of fence at any post spacing.

Draft — figures checked, awaiting an editorial read. Not indexed.

Formula: Sections = length ÷ post spacing, rounded up. Posts = sections + 1. Pickets = length in inches ÷ (picket width + gap).

What this calculates

This turns a length of fence into a materials list: posts, rails, pickets and the concrete to set the posts. The detail that catches people out is the post count. A run of fence needs one more post than it has sections, because both ends need one — a hundred foot run at eight foot spacing is thirteen sections but fourteen posts. Miss that and you are one post short at the very end of the job, which is exactly when the shop has closed.

How it works

Sections are the total length divided by the post spacing, rounded up, since a partial section at the end still needs its own pair of posts. Posts are sections plus one. Rails multiply the section count by the rails per section — two for a low fence, three for a standard six foot privacy fence, four for anything taller. Pickets are calculated from the total length in inches divided by the effective width of one picket, which is its actual width plus whatever gap you are leaving between them. Concrete assumes two 60 lb bags per post, the usual set for a 4x4 in a ten inch hole.

Worked example

A 100 foot privacy fence with posts every 8 feet, three rails per section, and 5.5 inch pickets butted tight. Sections: 100 ÷ 8 = 12.5, rounded up to 13. Posts: 13 + 1 = 14. Rails: 13 × 3 = 39. Pickets: 100 × 12 = 1,200 inches ÷ 5.5 = 219 pickets. Concrete: 14 posts × 2 bags = 28 bags of 60 lb, which is 1,680 pounds — worth knowing before you load the car.

Common mistakes

The off-by-one on posts, as above. Second, using nominal picket width instead of actual: calculating on 6 inches when the board is really 5.5 leaves you about 9% short on pickets. Third, forgetting that gates are not fence — a gate opening replaces a section but needs heavier posts on both sides, and the gate hardware is a separate purchase entirely. Fourth, assuming the ground is level; on a slope the rails either step or rake, and either way the picket count rises.

Common questions

How far apart should fence posts be?

Eight feet is the standard for wood privacy fence and matches common rail lengths. Six feet is stronger and worth it in high wind or on a slope. Ten feet is only really suitable for light ranch-rail fencing.

How deep should fence post holes be?

A third of the post length below grade is the usual rule — about two feet for a six foot fence — and always below the local frost line, or frost heave will lift the posts over a few winters.