If you are asking what size fence posts do I need, start with the finished fence height. Your posts must be long enough to support the fence above ground while leaving enough length below ground for a secure footing. You also need to choose a suitable post thickness, usually 3x3 or 4x4 for a domestic timber fence.

The right choice depends on more than height alone. Panel type, wind exposure, ground conditions, post spacing and whether you are supporting a gate all matter. This guide gives you practical starting points, but unusual or exposed sites may need a stronger specification.

What length fence post do you need?

A common rule is to put roughly one-third of a timber post into the ground. For many domestic fences, a depth of around 600mm is a practical minimum. Taller fences, heavy panels and exposed sites can require deeper holes and longer posts.

900mm fence: consider a post around 1.5m long, allowing approximately 600mm below ground.
1.2m fence: a post around 1.8m long will usually provide approximately 600mm in the ground.
1.5m fence: a post around 2.1m long gives approximately 600mm below ground.
1.8m fence: a 2.4m post is a common starting point, again allowing approximately 600mm below ground.
2.0m fence: you may need a post around 2.7m long so that you can increase the setting depth.

These are general guidelines rather than structural calculations. Check local planning rules before building a high boundary fence, particularly beside a road or pavement. Also remember that a gravel board adds to the total finished height. A 1.8m panel sitting on a 150mm gravel board creates a fence close to 1.95m high.

Should you choose 3x3 or 4x4 timber posts?

Both sizes are used for garden fencing, but they are not interchangeable in every situation. The measurements are commonly used trade descriptions, and actual finished dimensions can vary slightly depending on how the timber has been cut and treated.

When 3x3 timber posts may be suitable

A 3x3 timber post is often suitable for a modest-height, sheltered fence using relatively light panels. It can be a practical choice for low front garden boundaries, short runs and internal garden divisions where wind loading is limited.

Do not choose 3x3 simply because it is lighter or more economical. For a tall closeboard fence, solid panels or an exposed boundary, the extra strength of a larger post is usually worth considering.

When to use 4x4 timber posts

A 4x4 timber post provides more strength and rigidity. It is the usual safer choice for a fence around 1.8m high, heavier panels, exposed gardens and longer fence runs. It also gives fixings more timber to bite into, which can be helpful with rails and framed panels.

For a gate, use a properly sized gate post rather than assuming an ordinary fence post will cope. The post must carry the gate's weight and repeated movement. A wide or heavy timber gate can need a substantially larger section and deeper footing.

K C Fencing and Timber Ltd supplies suitable timber for trade and DIY fencing projects. If you tell us your fence height, panel style and site conditions, we can help you choose an appropriate stock size.

How deep should fence posts go?

For an ordinary domestic fence, around 600mm deep is widely used as a starting point. You may need to increase this to around 750mm or more for a taller fence, loose ground, a heavy gate or an exposed location. The hole should reach firm ground rather than stopping in soft topsoil.

Depth is only part of the footing. The hole must also be wide enough for adequate support around the post. A narrow hole with little concrete may not resist sideways movement, especially when solid panels catch the wind.

Keep these points in mind:

Check for buried cables, pipes and drains before digging.
Set every post upright and in line before the fixing material hardens.
Allow for the thickness of any gravel board when marking panel positions.
Avoid leaving a timber post in a pocket where water can collect.
Use treated timber intended for external fencing.

Ground conditions can change along the same boundary. Made-up ground, tree roots or old foundations may require a different approach. If you are unsure about safe excavation or footing design, ask a competent fencing contractor or builder for site-specific advice. K C Fencing and Timber Ltd supplies materials but does not install fencing.

How fence height and panel type affect post size

Two fences of the same height can put very different loads on their posts. A solid closeboard or overlap panel catches more wind than an open slatted or trellis design. Heavy-duty framed panels also place more weight between posts.

A 4x4 post is generally preferable where you are using full-height solid panels. In a very open garden, stronger posts, shorter spacing or concrete posts may be worth considering. Do not rely on a tall, flexible timber post where the fence regularly takes strong gusts.

Standard panels are often approximately 1.83m wide, but measure the actual products before setting posts. Your post centres must account for the panel width and the fixing method. Browse our fence panels and check the chosen panel dimensions before you start digging.

Timber posts or concrete posts?

Timber posts give a consistent timber appearance, are relatively easy to cut and accept screws and nails directly. Their service life depends on treatment quality, drainage, ground contact and ongoing care.

Concrete posts are heavier but do not rot at ground level. Slotted versions allow compatible panels and gravel boards to slide into place. They are often chosen for long-lasting panel fencing, particularly where future panel replacement needs to be straightforward.

If you choose concrete, post sizes and lengths are specified differently from 3x3 and 4x4 timber. Select a length that provides the required finished height and adequate setting depth. K C Fencing and Timber Ltd manufactures and supplies concrete posts, with delivery available across the West Midlands.

Remember gravel boards and the finished height

Gravel boards keep timber panels away from damp soil and can help extend their useful life. However, they increase the overall height of the fence. Include the board when calculating both post length and any planning limit.

For example, if you want a finished fence height of 1.8m and plan to use a 150mm gravel board, you may need a 1.65m panel rather than a 1.8m panel. Alternatively, using a full 1.8m panel will create a taller finished boundary.

Make your calculation from the final ground level, allowing for slopes and steps. On uneven ground, each bay may need checking separately. Compatible gravel boards are available in timber and concrete options.

A quick checklist before ordering

Measure the required finished fence height.
Add the height of any gravel board.
Choose 3x3 for suitable lighter, lower and sheltered fencing, or 4x4 for greater strength.
Allow at least around 600mm below ground in typical domestic conditions, increasing where necessary.
Consider solid panels, wind exposure, slopes and soft ground.
Use a stronger, correctly sized post for a gate.
Confirm panel widths and post centres before digging.
Check planning restrictions and underground services.

As a simple starting point, a 1.8m domestic fence commonly uses 2.4m-long 4x4 timber posts, with around 600mm set below ground. Treat that as guidance, not a universal answer: exposed sites, weak ground and heavy fencing may require longer or stronger posts.

Order fence posts from K C Fencing and Timber Ltd

K C Fencing and Timber Ltd manufactures and supplies fencing materials to trade and DIY customers across the West Midlands. Delivery is available throughout the region, including Wolverhampton, Birmingham, Walsall, Dudley, West Bromwich, Worcester, Redditch, Stourbridge, Kidderminster and Halesowen. You can also collect free from our yard at 83 Portway Road, Wednesbury WS10 7DZ.

For help choosing the right post size and quantity, call 01902 288162 or request a quote.

What Size Fence Posts Do I Need?