Advanced options
Based on standard 6ft (1.83m) wide panels with a post at each end of every panel. Use concrete or 2.4m timber posts sunk 600mm; postcrete needs roughly one bag per post, two for exposed runs.
What The Fence Calculator Works Out
- Fence panels: the run length divided by the panel width (a standard UK panel is 6ft, 1.83m), rounded up. A 20m run is 11 panels. The odd remainder is normal: panels cut down easily for the final bay, and it is far better to order the extra panel than to stretch the spacing.
- Posts: one more than the number of panels, so 12 for 11 panels. Concrete posts outlast timber by decades and make future panel swaps a two-minute lift-out job; timber posts look softer but should be sunk 600mm into postcrete.
- Gravel boards: one per panel. These 150mm concrete or timber strips keep the panel clear of wet ground and are the difference between a fence that lasts and one that rots from the bottom.
- Rules before ordering: fences above 2m generally need planning permission (1m beside a highway), the boundary and who owns the fence is a deeds question, and panels face the neighbour with the rails on your side by convention.
- Panel width (advanced): change the 1.83m default for 1.8m metric panels, 0.9m half panels or closeboard bays set to your own post spacing.
- Fence height and post length (advanced): post length is the fence height plus the gravel board plus 600mm in the ground, rounded up to a stock length. A 6ft fence with gravel boards needs 2.7m timber posts (2.4m if you accept less in the ground); concrete slotted posts are sold to match the panel height.
- Posts and ground (advanced): sets the postcrete at one 20kg bag per post for timber in sheltered ground, two for exposed or soft ground and for heavier concrete posts. Dig below any turf line to firm ground, and on slopes step the panels rather than raking them.
- Gates (advanced): each gate takes about 1m out of the panel run and adds one extra post to the line. Gate posts should be heavier section and set in two bags of postcrete.
- Materials cost and cost per metre (advanced): panels, posts, gravel boards and postcrete at your prices. Typical UK prices are GBP 30 to GBP 60 for a 6ft lap or closeboard panel, GBP 10 to GBP 25 per post and GBP 8 to GBP 15 per gravel board. The per-metre figure is materials only; installation commonly adds GBP 60 to GBP 100 per bay.
Source and further reading: GOV.UK: planning permission for fences.