The standard rule is to bury fence posts to a depth of one-third of the total post length, or one-third of the fence height plus 150mm (6 inches) for a frost buffer. For example, a 6ft (1.8m) fence typically requires posts set at least 600mm (2ft) deep in firm soil, and 750–900mm (2.5–3ft) in soft or clay-heavy ground. Gate posts and corner posts should always be set deeper than standard line posts.

The volume of concrete needed per post hole is: π × (hole radius)² × hole depth. For a typical 6ft fence with a 250mm wide hole at 700mm deep, that’s approximately 34 litres (0.034 m³) per post. A standard 20kg bag of post-mix concrete makes about 15–18 litres of set concrete. For a project-wide total, multiply per-post volume by number of posts and add 10% wastage.

The one-third rule states that the buried portion of a fence post should be at least one-third of the total post length. So a 2.4m post should be set at least 800mm into the ground, leaving 1.6m above ground. This ensures adequate leverage resistance against wind loads. For exposed, coastal, or high-wind locations, increasing burial depth to 40% of total length significantly improves stability.

Yes, significantly. In firm, well-drained loam or chalk, the standard one-third rule applies. In soft, sandy, or waterlogged ground, posts should be set 25–50% deeper and always set in concrete. Clay soils expand and contract with moisture changes, which can cause posts to lean over time — deeper holes with concrete collars that taper above ground level help prevent this. In rocky ground, you may need less depth but professional drilling equipment.

Concrete provides the strongest and most stable fixing for fence posts and is recommended for all wooden posts over 1.2m and any post carrying significant wind or lateral loads. Gravel or dry-pack filling can work for light decorative fencing in firm, free-draining soil, as it allows moisture to drain away from the post base and reduces rot. For maximum post life, treat all buried post sections with preservative and use gravel at the base under the concrete collar to improve drainage.

Post holes should be at least 2–3 times the width of the post. For a 75×75mm (3×3 inch) post, dig a hole at least 150–225mm (6–9 inches) wide. For a 100×100mm post, aim for 200–300mm. The wider the hole, the more concrete mass anchoring the post, which improves stability in soft ground. A post-hole borer (handheld or tractor-mounted) produces the cleanest, most consistent holes.

For a 6ft (1.8m) fence, you need posts that are at least 2.4m (8ft) long in good soil — this gives 1.8m above ground and 600mm in the ground. In softer soil where 900mm depth is needed, buy 2.7m posts. Always buy posts slightly longer than the calculation suggests, as you can trim them to a consistent height after installation but cannot add length to a post that is too short.

Standard fence panel spacing is 1.8m (6ft) centre-to-centre, as most fence panels in the UK are manufactured in this width. For close-board fencing, posts are typically spaced 1.8–3m apart. Gate posts must be spaced to match the gate width plus clearance for hinges and latches. In very exposed or high-wind locations, reducing post spacing to 1.5m significantly improves fence stability and resistance to storm damage.