A fence that leans, rattles or wobbles is nearly always a post problem, not a panel problem. The panels might look fine on day one, but if the posts are not set deep enough, the whole run can move the first time you get wind and rain. Getting the post depth right is the unglamorous bit that makes everything else easier.
UK gardens vary a lot. Clay can hold water and shift, sandy soil can slump, and made-up ground can be full of loose fill. That is why advice online can feel inconsistent. We keep it simple. For domestic fencing, we advise a post depth of 600mm for all and any fence post, and we build around that as a reliable baseline.
This guide covers how to apply a 600mm post depth in real gardens, how to space posts so panels fit properly, and a practical way to estimate how much Postcrete you will need. Think in systems: fence panels, fence posts, gravel boards, ironmongery for fixings, and cement products for setting everything properly.
Before you dig, take care around underground services. If you are unsure where cables or pipes run, check first and dig cautiously.
Post hole depth and why we stick to 600mm
For most garden fencing jobs, 600mm gives you a strong, repeatable standard. It is deep enough to resist everyday wind load, it works well with common post lengths, and it keeps your method consistent across the run. Consistency matters. A fence is only as straight as its weakest post.
The key is to treat 600mm as the depth you set the post into the ground, not the overall hole depth you happen to dig on the day. On uneven ground you might dig a little deeper to remove soft material, but the post should still be set so that around 600mm of it is below finished ground level at that position.
If your garden slopes, measure from the ground level where each post sits. Do not measure from the highest point nearby. That is how fences end up short on one end and wobbly on the other.
Hole width, concrete and getting a solid set
Depth is only part of the story. Your hole needs enough width for the concrete to grip the post and lock it in place. As a practical guide, aim for a hole width that gives you a decent collar of concrete around the post. Too narrow and you struggle to get strength. Too wide and you burn through Postcrete without gaining much.
In most gardens, a hole in the region of 200mm to 300mm wide works well for fence posts. If you are setting a gate post, go wider. Gates twist hinge posts every time they open, so give the concrete more mass to work with.
Brace each post and check it with a level from two sides while the concrete firms up. Quick-set mixes still need time to stabilise. Most posts that end up out of plumb were fine at the start and drifted while the mix was going off.
Post spacing and keeping the run straight
The easiest way to avoid headaches is to space posts to suit the fence panels you are fitting. Most fence panels are made for standard bays, so match your post centres to the panel width and keep the line tight. A snug fit and proper fixings reduces rattle and movement.
If your run length does not divide neatly, it is usually better to plan a shorter bay at one end than to spread the mismatch across the whole line. Small errors add up. They make the fence look uneven and can leave you fighting gaps at the final bay.
Heavier panels, such as closeboard fence panels, put more strain on the posts than lighter overlap panels. If you are using heavier panels, choose sturdy fence posts and do not cut corners on the concrete. A solid post set to 600mm gives the panel something stable to hang from.
Clay, sand and wet ground: what changes
Different ground conditions change how you work, not the target depth. In clay, the problem is movement. It can soften in wet weather and shrink in dry spells. Keep the post set at 600mm and take extra care to brace it well while setting. If you are digging into very soft clay, remove the worst of it before you concrete.
In sandy soil, the issue is collapse. The hole sides can fall in as you dig, and you can end up pouring concrete into loose material. Dig cleanly, keep the hole shape as consistent as you can, and brace the post firmly so it cannot shift as the mix fills the voids.
In very wet ground, standing water at the bottom of the hole can weaken the set while it cures. Scoop out excess water where possible, and consider improving drainage along the fence line. If a spot is permanently boggy, concrete fence posts can be a sensible option for a more permanent system.
How much Postcrete do I need per post?
The amount of Postcrete depends on the hole width and how much of the hole you fill with concrete. With a 600mm depth, the main variable is diameter. Larger holes use more mix, especially for gate posts and poor ground.
As a rough guide, a 200mm wide hole filled to 600mm deep is around 19 litres of concrete. A 250mm hole at 600mm deep is around 29 litres. A 300mm hole at 600mm deep is around 42 litres. These figures are a practical estimate rather than an exact promise, because mix yield varies with moisture and how the hole is shaped.
For most domestic fence posts, you will often find you are using roughly one to three 20kg bags per post, depending on hole width and whether you are setting a gate post. If you are doing a full run, it is usually safer to buy an extra bag or two than to end up short and start shrinking holes to make the bags stretch.
Tips to build it right first time
Set out your line before you dig. A string line and a tape measure helps you keep the fence straight, and it makes spacing far easier. Mark post centres, check for steps on slopes, and plan where the fence starts and ends so you do not get caught out at the last bay.
Use gravel boards where they make sense. They protect the bottom edge of timber fence panels and keep the fence looking tidy when soil or gravel builds up along the line. They also make maintenance easier, because you can keep the timber clear of ground contact.
Think through the full kit before you start. Plan fence panels, fence posts, gravel boards, ironmongery and cement products together so you have the right sizes and fixings on site. If you are fitting a garden gate, treat the hinge post as a separate job and give it extra width and concrete so it stays true over time.
