How Deep Should Fence Posts Go? A Tradesman's Guide for UK Gardens

A leaning fence is one of the most common calls we get, and nine times out of ten the problem is the same: the posts weren't set deep enough. Get the depth right and a properly installed fence will shrug off a decade of British weather. Get it wrong, and you'll be propping it back up after every autumn gale. Here's what depth fence posts actually need — and why it matters more than the timber you buy.

The Rule of Thumb: A Third In, Two Thirds Above

The time-served standard for fence post depth is that roughly one third of the total post length should be buried in the ground, with two thirds showing above. So for a 6ft (1.8m) fence, you want a post around 2.4m long with 600mm in the ground. That's the foundation for most garden fences in the UK, and it's what we'd set on a standard residential installation in Bristol, Gloucester or anywhere else we cover.

This isn't an arbitrary figure. A fence post acts like a lever — the taller the fence, the greater the force wind applies at the top, and the more the base wants to pivot. The deeper the anchor, the more of that force is absorbed by the surrounding ground rather than transmitted as movement.

Post Depth by Fence Height

As a practical guide across common UK fence heights:

• 3ft (900mm) fence: post around 1.5m long, 450–600mm in the ground
• 4ft (1.2m) fence: post around 1.8m long, 600mm in the ground
• 5ft (1.5m) fence: post around 2.1m long, 600mm in the ground
• 6ft (1.8m) fence: post around 2.4m long, 600–750mm in the ground
• Over 6ft: 750mm minimum, and we'd often step up to a heavier section or add a concrete spur

If you're in an exposed location — on a hilltop, near the coast, or with no windbreak from buildings or mature planting — bump the depth up by 150mm. The cost of extra concrete is nothing compared to replacing panels after a storm.

Concrete, Postcrete or Rammed Hardcore?

We almost always set fence posts in concrete. Postcrete is the branded ready-mix that sets in minutes — it's convenient for one or two posts in a domestic job, and it does a perfectly good job for most garden fences. For a full run of posts we tend to mix our own ballast and cement because it works out more economical and we can control the mix for wetter ground.

Rammed hardcore alone is occasionally used for rural agricultural fencing where aesthetics don't matter, but for a garden fence in a private or residential setting, concrete is the only way to get the life we'd want out of it.

One thing worth mentioning: don't fill the hole right to the surface with concrete. Bring it up to about 75mm below ground level, then cap with soil or gravel. That way rainwater drains away from the base of the timber rather than pooling against it, which is what causes the rot line you see at the bottom of old fence posts.

Concrete Posts vs Timber Posts

Concrete posts are noticeably more expensive upfront but they'll outlast three timber posts, don't rot at the ground line, and are effectively fit-and-forget. We recommend them strongly for boundary fences where you don't want to be revisiting the job in ten years. Timber posts are fine for decorative or screening fences, but if they're supporting full close-board panels, concrete gives you a much longer-lived result.

Drainage and Ground Conditions

Clay soils expand and contract with rainfall. On heavy clay — common across the Severn Vale and parts of Cardiff — we'd usually err on the deeper side and add a little extra gravel at the base of the post hole to let water drain away. On sandy or chalky ground, drainage is less of an issue but the ground itself gives less resistance, so again we'd go deeper rather than wider to maintain stability.

Frequently Asked Questions

Can I set fence posts in just earth?
Only on temporary or agricultural fencing with short posts. For anything structural or for a fence you want to last, concrete or a concrete spur is the correct approach.

How long does concrete need to set before hanging panels?
With postcrete, you can usually hang light panels after a couple of hours. With traditional concrete mix, we give it at least 24 hours before loading with panels, and up to 48 in cold weather.

How deep should a gate post be?
Gate posts take more strain than regular fence posts because they carry the gate's weight and the shock of opening and closing. We typically bury them 150–300mm deeper than the run posts, with a larger concrete plug.

Can I reuse old post holes?
Usually no — by the time a post has rotted through, the ground around it is disturbed and won't grip a new post properly. It's almost always better to dig a fresh hole 300mm offset from the old one.

Get It Right the First Time

A correctly installed fence should give you 15–20 years of service with minimal attention. If you're replacing an old fence or starting from scratch, we're happy to visit, advise on the right specification for your property, and give you a fixed-price written quote with no obligation. See our full fencing service or get in touch for a free site visit.