Fence post length calculator
Work out what length fence posts you need based on your fence panel height, gravel board height and any trellis fitted above the panel.
Enter your fence height details
Select the visible parts of your fence. The calculator adds them together, then adds 600mm to allow for the section of post set into the ground.
Your fence post estimate
Use this as a guide when choosing fence posts. Always check the finished height, ground conditions and installation method before ordering.
| Item | Height allowed | Notes |
|---|---|---|
| Fence panel | 0mm | Selected fence panel height. |
| Gravel board | 0mm | Included if selected. |
| Trellis | 0mm | Included if selected. |
| Below ground allowance | 600mm | Standard allowance added to the visible fence height. |
| Suggested post length | 0ft | Rounded up to the next suitable post length. |
Recommended next steps
Choose the right post type and matching fencing materials for your layout.
How this fence post length calculator works
A fence post should be longer than the finished fence height because part of the post needs to sit below ground. This calculator adds your fence panel height, gravel board height and trellis height together, then adds 600mm.
For example, a 6ft fence panel with a 150mm gravel board gives a visible fence height of around 1,979mm. Add 600mm below ground and the minimum post length is around 2,579mm, so the calculator would suggest rounding up to a 9ft post.
Choosing the right fence posts
Concrete fence posts are a strong, long lasting choice for many garden boundaries. Wooden fence posts are often chosen where a softer timber finish is preferred. For exposed gardens, taller fences or heavier fence runs, it is worth checking the layout carefully before ordering.
You can pair this tool with our fence panels, gravel boards, fence posts, trellis panels and cement products to plan the full run.
| Visible fence build up | Typical post length guide |
|---|---|
| 6ft panel only | Usually 8ft post |
| 6ft panel plus 150mm gravel board | Usually 9ft post |
| 5ft panel plus 150mm gravel board | Usually 8ft post |
| 4ft panel plus 150mm gravel board | Usually 7ft post |
Fence post length calculator FAQs
How long should fence posts be?
As a simple guide, fence posts should be around 600mm longer than the visible fence height. The visible height includes the fence panel, gravel board and any trellis fitted above the panel.
Do gravel boards affect fence post length?
Yes. A gravel board increases the finished height of the fence, so it should be included when working out the post length. A 150mm gravel board adds 150mm to the visible height.
Does trellis affect fence post length?
Yes. If trellis is fixed above the fence panel, its height should be included in the overall visible fence height before adding the below ground allowance.
Is 600mm always enough below ground?
600mm is a common allowance for many standard garden fence posts. Exposed sites, soft ground, heavy gates and taller fence runs may need extra care and a more robust installation.
Should I use concrete or wooden fence posts?
Concrete fence posts are a strong, durable option for most standard garden boundaries. Wooden fence posts are useful where you want a matching timber look. The right choice depends on the fence style, site conditions and the finish you prefer.