Fence Calculator

A fence is quoted by the metre but built from posts, rails and panels, and only the panels scale directly with length. Posts come every 2 to 3 m, so a 30 m run is 11 posts at 3 m spacing but 16 at 2 m. Moving from 3 m to 2 m costs 45 % more posts and adds no extra panel, which is why the spacing question matters more than the total length.

Rails are counted per bay and usually two per bay for a panel fence, three for a closeboard fence. A bay is the space between posts, so a 30 m run at 2.5 m gives twelve bays and twelve panels, but posts are only thirteen including both ends.

A 1.8 m closeboard fence catches a lot of wind: at 20 m/s the load on a 30 m run is measured in tonnes, and it is transferred entirely through the posts into the ground. That is why post depth matters more than post spacing on an exposed site, and why a concrete spur or a metpost in soft ground fails before the panel does.

Lowering the fence to 1.2 m reduces the wind load by roughly half. It is the cheapest engineering decision available, and it is made before the first hole is dug.

Gravel boards and concrete plinths are counted by the running metre, gates by the piece, and both are usually excluded from a panel quote. A single gate replaces a panel plus one bay, and its posts need to be heavier than the line posts because the gate hangs and swings on them.

Leave a gap under the panels for air and drainage. A fence built tight to the ground rots at the bottom rail within a few years, and replacing a bottom rail on a standing fence costs more than the gap ever would have.