Fence Calculator (UK)
Last updated: 12 August 2026
Work out the materials for a panel fence: how many panels and posts, gravel boards, and how many bags of postcrete to set the posts.
How the calculation works
Panels = fence length ÷ panel width, rounded up. You always need one more post than panels, because each panel sits between two posts and the run needs a closing post.
Posts should be buried at least 600mm for a 1.8m fence — a third of the above-ground height is the traditional rule. Postcrete is estimated at two 20kg bags per post for a 6ft fence, less for lower fences with smaller holes.
Fence post depths and sizes
| Fence height | Post length | Depth in ground | Postcrete per post |
|---|---|---|---|
| 1.2m (4ft) | 1.8m | 600mm | 1–1.5 bags |
| 1.5m (5ft) | 2.1m | 600mm | 1.5 bags |
| 1.8m (6ft) | 2.4m | 600mm+ | 2 bags |
Use 100 × 100mm posts for 6ft fences in exposed positions; 75 × 75mm is adequate for lower fences. Concrete posts with gravel boards last far longer than timber in wet ground.
Fence height and planning rules
In England and Wales you can generally build a fence up to 2m high without planning permission, dropping to 1m if it fronts a road used by vehicles. Boundary ownership and party wall considerations matter too — check the deeds and talk to your neighbour before starting.
Frequently asked questions
How many fence panels do I need?
Divide your fence length by the panel width. Standard UK panels are 1.83m (6ft) wide, so a 20 metre run needs 11 panels. You always need one more post than panels — 12 in this case.
How deep should fence posts go?
At least 600mm for a 1.8m (6ft) fence, which means a 2.4m post. The traditional rule is to bury a third of the above-ground height. Go deeper in exposed or windy positions and in soft ground.
How many bags of postcrete per fence post?
Two 20kg bags per post for a standard 6ft fence, or about 1.5 bags for lower fences with smaller holes. Postcrete sets in around 10 minutes, so mix in the hole and have the post plumb before you pour.
How high can a garden fence be without planning permission?
Generally up to 2m in England and Wales, or 1m if the fence borders a road used by vehicles. Different rules apply to listed buildings and conservation areas, so check with your local authority.
Do I need gravel boards?
They are strongly recommended. Gravel boards keep the bottom of the panel out of wet soil, which is where fences rot first, and they are far cheaper to replace than a whole panel.
Related calculators
Postcrete Calculator
Bags of post mix per fence post, by hole and post size.
Decking Calculator
Boards, joists and screws for a timber or composite deck.
Turf Calculator
How many rolls of turf for your lawn, plus topsoil.
Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.