Fence Post Calculator — How Many Posts

Bury roughly one-third of the above-ground height. A 1.8m (6ft) fence needs a 2.4m post with 600mm in the ground; a 1.2m fence needs about 400–600mm buried. Go deeper on exposed sites or in soft, sandy soil.

Divide the fence run by the panel width (a standard 6ft panel is 1.83m) and round up to get the number of panels, then add one — every run needs one more post than it has panels to close both ends.

Timber: 75 × 75mm for fences up to 1.5m, 100 × 100mm for 1.8m or heavier panels. Concrete: 100 × 125mm slotted posts that the panels slide into. Metal: 50–60mm box-section steel.

Timber is cheapest and easiest to cut on site. Concrete lasts longest and resists rot, with slotted versions holding panels without nails. Metal posts suit modern designs and are light to handle.

Dig a hole around 300mm wide to the buried depth, add ~75mm of gravel for drainage, place the post, check it is vertical, then fill with postcrete or concrete to ground level. A 300mm × 600mm hole takes roughly 2 × 20kg bags of postcrete. Allow 24 hours to set before fixing panels.

Yes, bolt-down or spike-driven post supports are quicker and avoid digging. They work well in firm ground but are less stable in soft or clay soils and on taller fences.