What actually affects how much fence material you need
Post spacing drives almost every other quantity in a fence project, and it varies by style and material. Wood privacy fencing typically uses 8-foot spacing between posts, but taller fences or high-wind areas often need posts closer together — every extra post also adds a hole, a bag of concrete, and extra rail length. Post depth matters just as much as spacing: as a rule of thumb, at least a third of the post length should be below ground, and in cold climates the hole needs to reach below the local frost line or the post can heave over winter. Gate openings need their own math — gate posts are typically set in larger, deeper holes than line posts because they carry more lateral stress from the swinging gate. Board style changes waste too: dog-eared and pointed pickets both use standard board widths but lose a bit of usable length to the cut, so budget slightly more board footage for a picket fence than for a flat-top privacy fence of the same length.
How to calculate fence materials
Fence material quantities start with post count, then derive rails and boards from post spacing:
posts = ceil(fence length ÷ post spacing) + 1 spans = posts − 1 rails = spans × rail count × ceil(spacing ÷ 8 ft) boards = ceil(fence length × 12 in ÷ board width) × (1 + waste%)
Concrete: 2 × 60 lb bags per post. Rails are priced as 8 ft treated lumber; privacy boards as 1×4 dog-ear boards. Always add extra boards for future repairs.
Common mistakes
- Setting posts too shallow — must go below frost depth to prevent heaving in cold climates.
- Installing before calling 811 — always request a utility locate before digging post holes.
- Not checking property lines — a fence on the neighbour's property is a legal problem.
- Using non-ground-contact lumber for posts — use UC4B or UC4C rated PT for in-ground use.