Post Depth, Spacing and How Much Postcrete You Need

A fence can look solid when it first goes up, but what really decides how well it lasts is how the posts are set. If the posts are not deep enough, straight enough or properly concreted in, the whole fence can start to move over time. That is when you get leaning posts, rattling panels and a fence line that never quite feels right again.

At CE Clarke Fencing, for most standard domestic fencing, we treat around 600mm of the post in the ground as a good practical starting point. It is a sensible depth for many garden fencing jobs in the UK and gives you a reliable base to build from.

That does not mean every fence should be done exactly the same. Ground conditions, exposure, fence type and whether you are hanging a gate all make a difference.

In this guide, we look at post depth, spacing, how much Postmix/Postcrete you may need, and how fence post advice differs around the world depending on soil, weather and climate.

Before you start digging, always take care around buried pipes, cables and other underground services.

Domestic Fence Post installation on a site in Norfolk

How Deep Should a Fence Post Be?

For most domestic garden fencing in the UK, 600mm (2ft) in the ground is a good practical starting point.

That is a common depth for standard fencing work and helps give the fence enough support to cope with normal wind, weather and general movement in the ground. It also keeps the job consistent. If every post is set properly and to a similar standard, the whole fence line has a much better chance of staying straight, firm and secure.

The important thing is to measure from the finished ground level where each post actually sits.

If your garden slopes, every post position needs to be judged from that point. Do not just measure from the highest point nearby or assume every hole will be the same. That is where uneven fence lines and weak spots begin.

It is also worth saying clearly that 600mm is a sound starting point, not a one-size-fits-all rule for every fence.

For most standard domestic fencing, around 600mm in the ground is a good starting point — but gates, heavy panels, banks, ditches and poor ground can all mean you need more.

When You May Need to Go Deeper

Some fencing jobs need more depth than others.

• gate posts
• heavier fence panels
• very exposed areas
• soft, loose or made-up ground
• fences taking more strain than normal
• fencing on banks, slopes or near ditches

A gate post is one of the clearest examples. Gates put repeated movement and twisting force on the hinge post, so that side often needs a wider and deeper foundation than a normal post in the run.

The same goes for heavier fencing. If you are fitting strong closeboard fence panels, the fence needs a solid base below ground as well as strength above it.

Why Hole Size Matters Too

It is not just the depth that matters. The hole also needs to be wide enough for the concrete to support the post properly.

For many domestic fence posts, a hole around 200mm to 300mm wide is a sensible guide. That gives enough concrete around the post to help lock it in place without going overboard.

If the hole is too narrow, there may not be enough concrete around the post to create a proper hold. If it is too wide, you can get through far more Postcrete than necessary without a huge gain in strength.

For gate posts, going wider is usually worthwhile.

Once the post is in position, brace it properly and check it with a level from at least two sides. A lot of fencing problems come from posts that were straight when they went in, but moved while the concrete was setting.

Fence Post Spacing

Fence post spacing should always suit the fencing system you are installing.

In simple terms, the spacing needs to match the actual panel size and fixing method you are working with. Slotted concrete posts, timber posts with brackets and built-up bays can all vary slightly, so it is worth checking real dimensions before digging.

If the full run does not divide perfectly, it is usually better to adjust one bay than to spread small errors across the whole fence line. Otherwise the final section is often where the problem shows itself.

The simplest way to keep things right is to:

• firstly, ensure you are working safely, find and mark out all services
• set a string line
• mark your post centres properly
• measure carefully before digging the full run

Good setting out saves time, materials and headaches.

setting out with a string line, blue spray de-marking a known electricity service

Ground Conditions Make a Big Difference

Part of the reason fencing advice varies so much is that the ground itself can vary so much.

Clay Ground

Clay can hold water, soften in wet weather and shrink back in dry conditions. It can move more than people expect. In clay, good bracing and a proper set matter even more.

Sandy or Loose Ground

Loose or sandy soil can collapse back into the hole as you dig. That can affect the shape of the hole and the way the concrete sits around the post. In those conditions, it pays to work carefully and keep the post well supported while setting.

Wet or Boggy Ground

Very wet ground makes any fencing job harder. Soft ground around the hole can weaken the support, and standing water can make things awkward while setting the post. In some locations, concrete fence posts can be a sensible longer-term option, but whatever post type you choose, the installation still needs to be done properly.

Fencing on a Bank, Slope or Next to a Ditch

Fencing on a bank, slope or next to a ditch often needs more care than fencing on flat, solid ground. In these situations, the issue is not just normal post stability. You are also dealing with the risk of the ground giving way, washing out or gradually moving over time.

If a fence is being installed close to the edge of a ditch or on the side of a bank, the posts may need to go deeper than a standard domestic starting point to give the fence a better chance of staying upright and secure. This is especially important in made-up ground, where the soil may have been previously disturbed, built up, filled, or left looser than natural ground.

Made-up ground can look firm on the surface but still be weak underneath. If the ground is soft, loose or prone to movement, a shallow post hole can leave the fence vulnerable to leaning, slipping or gradually pulling towards the ditch or down the bank.

In these conditions, it is often worth treating the job differently from a normal straight run across level ground. Deeper holes, better support and taking extra care with the line of the fence can make a big difference to how well it holds up long term.

Fencing on made-up-ground bank that required 4 foot deep post foundations

Practical site tip

If a fence line is close to a ditch or running along a bank, do not assume your usual depth will be enough. Weak or disturbed ground can pull a fence out of line over time, even if everything looked fine when first installed.

How Much Postcrete Do You Need Per Fence Post?

The amount of Postcrete needed depends mainly on the size of the hole.

As a rough guide, for a hole 600mm deep:

• a 200mm wide hole takes about 19 litres
• a 250mm wide hole takes about 29 litres
• a 300mm wide hole takes about 42 litres

These are working estimates rather than exact figures, because real fence post holes are rarely perfect and ground conditions can affect how much concrete you use.

In practice, many domestic fence posts use around one to three 20kg bags of Postcrete per post, depending on the size of the hole and whether it is a standard post or something heavier, such as a gate post.

If you are ordering materials for a full fence run, it is normally better to allow a little extra than to come up short at the end.

How Fence Post Depth Differs Around the World

Fence post depth is not talked about the same way everywhere, and that is largely because weather, soil and climate vary so much from country to country.

In the UK, for most domestic garden fencing, the conversation is usually about finding a practical depth that gives good support in typical conditions. That is why a figure like 600mm is often used as a sensible starting point for standard jobs.

In parts of the United States, the advice is often different. A common rule of thumb there is to bury around one-third of the post length, but in colder parts of the country the bigger issue is often the frost line. In areas where the ground freezes deeply in winter, shallow posts can be affected by frost heave, where the freezing and thawing of the soil gradually pushes posts upward or shifts them out of line. That is why in some parts of the US, posts or footings may need to go much deeper than what would usually be discussed for a standard garden fence in Britain.

In colder parts of Canada and parts of northern Europe, the same general issue can apply. The deeper the ground freezes, the more important frost depth becomes.

In hotter or drier parts of the world, the challenge may be completely different. Instead of frost, the concern might be very dry soil, loose sandy ground, or ground movement caused by long wet and dry cycles. In those places, the right post depth is still important, but the reason behind it can be different.

That is why there is no single global rule that suits every fence everywhere. Local conditions matter. Climate matters. Ground matters. The best fence post depth is always the one that suits the job, the location and the type of fence being built.

A Few Simple Tips Before You Start

If you want a fence to stay straight and solid, a few basics make a big difference.

• Set the line out before you dig
• Use a string line and mark your centres clearly
• Measure each post position properly, especially on sloping ground
• Use gravel boards where needed to help protect the bottom of timber panels from sitting against soil
• Think about the full fence system together: panels, posts, gravel boards, fixings and Postcrete
• If you are fitting a gate, treat that post as a more demanding part of the job