How deep should fence posts be?

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.

How many posts do I need?

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.

What size posts for panel fencing?

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, concrete, or metal posts?

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.

How do I set fence posts in concrete?

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.

Can I use metal post supports instead of concrete?

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.

GardenCalcs

Fence Post Calculator — How Many Posts

Work out the number of fence posts and spacing for your fence run.

Fence Length

Total length of the fence run in metres.

Fence Height

Above-ground panel height. UK standard panels are 0.9, 1.2, 1.5 or 1.8m (6ft). Stay at or below 2m to avoid needing planning permission.

Post Spacing

Centre-to-centre distance between posts — this is the panel width. A standard 6ft panel spans 1.83m.

Post TypeSets the recommended post section. Timber is cheapest, concrete lasts longest, metal suits modern designs.

How We Calculate This

Panels = Fence Length ÷ Post Spacing, rounded up (a standard 6ft panel is 1.83m wide). Posts = Panels + 1, because every run needs one more post than panels to close both ends. Post Length = Fence Height + buried depth, where the buried depth is about one-third of the above-ground height (1.8m fence → 600mm buried → 2.4m post). The recommended post section follows the post type and fence height.

Frequently Asked Questions

Related Calculators

Fence Panel Calculator

Calculate how many fence panels you need for your boundary.

Gravel Board Calculator

Calculate gravel boards needed to protect fence panels from rot.

Trellis Calculator

Work out trellis panel quantities and fixing requirements.

Edging Calculator

Calculate lawn or border edging quantities for straight and curved runs.

Sleeper Calculator

Work out how many railway sleepers you need for raised beds or retaining walls.

Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.