How it's done
Concrete Fence Post Sizes and Depths Explained
For a standard 1.8m garden fence the usual concrete post is around 2.4m long, with roughly 600mm in the ground and a concrete base of about 700 to 750mm deep set around it.
Concrete fence posts come in a handful of standard lengths and profiles, and choosing the wrong one is the usual reason a new fence ends up too short, too tall or leaning within a couple of winters. The post you need depends on the fence height, the style of fence and the ground it goes into.
This guide explains the common sizes, how deep posts should go, and how concrete posts compare with 100 by 100 timber posts. It reflects how we set posts on jobs across London and Hertfordshire.
Common concrete post lengths
The rule of thumb is that a post should be the fence height plus around 600mm for the part in the ground. That is why the 2.4m post is the most common: it suits a 1.8m fence with gravel boards. Shorter posts suit lower fences, and longer posts are used where trellis goes on top or the ground falls away.
| Fence height (with gravel board) | Typical post length |
|---|---|
| 0.9m to 1.0m | 1.5m to 1.8m |
| 1.2m | 1.8m |
| 1.5m | 2.1m |
| 1.8m | 2.4m |
| 1.8m plus trellis | 2.7m or longer |
Slotted, mortice and repair spurs
Slotted posts have a channel down each side for panels and gravel boards to drop into, and are the standard choice for panel fencing. Mortice posts have holes for the rails of a closeboard fence. Repair spurs are short concrete posts bolted beside a broken timber post; they are a stopgap rather than a long term fix.
- Slotted intermediate posts for panel runs
- End and corner posts slotted on one or two faces
- Mortice posts for closeboard rails
- Repair spurs for temporary fixes to timber posts
How deep concrete posts should go
The part of the post in the ground is only half the story. What holds it is the concrete around it. On our jobs a 2.4m post for a 1.8m fence sits in a concrete base of around 700 to 750mm deep, wider at the bottom than a quick bucket of postcrete. Soft ground, slopes and exposed sites may need deeper or wider bases, which we judge on the visit.
Concrete or 100 by 100 timber?
Timber posts for a garden fence are usually 100 by 100mm pressure treated. They look softer and can be cut on site, but they rot at ground level in time. Concrete posts do not rot and, with a gravel board, keep all the timber off the soil. Our guide on concrete or wooden fence posts compares them in more detail.
Spacing
Posts for panel fencing are spaced to the panel width, typically 1.83m centres. Closeboard allows a little more flexibility because the rails are cut to length, but posts should still be close enough to carry the wind load on a solid fence.
Frequently asked
What size concrete post do I need for a 6ft fence?
A 6ft (1.8m) fence normally uses a 2.4m concrete post.
How deep should a concrete fence post be?
Around 600mm of post in the ground, set in a concrete base of about 700 to 750mm deep for a 1.8m fence.
How long is a 10ft concrete post used for?
Around 3m posts are used for taller fences, usually with trellis on top or where the ground falls away.
Are concrete posts better than timber?
They last longer because they do not rot, but they are heavier and less forgiving to cut. Timber suits some styles better.
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