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Work out how many fence panels, posts, gravel boards and bags of Postcrete you need. Choose the panel height, the posts and the gravel board, enter the length of the fence and press Calculate to see the full list, the post length to buy and the finished height.
| Panel | Fence Height | Post | Postcrete Bags |
|---|
The same run with each panel height, using your posts and gravel board. Fence height includes the gravel board.
You get the number of panels and whether the last one needs cutting, the number and length of posts, the end, corner and intermediate posts for concrete fencing, the gravel boards, the bags of Postcrete and, for timber posts, the clips and post caps. A table shows the same run with each panel height, and you can copy the list or save it as a PDF.
Each panel is 1.83 m wide and sits between two posts, so a fence is a row of panels with one more post than panels. The posts add their own width, about 100 mm for concrete and 4 × 4 timber posts, so each bay takes up about 1.93 m.
Panels = (fence length − post width) ÷ (1.83 m + post width), rounded up · Posts = panels + 1
| Fence length | Panels | Posts |
|---|---|---|
| 5 m | 3 | 4 |
| 10 m | 6 | 7 |
| 15 m | 8 | 9 |
| 20 m | 11 | 12 |
| 25 m | 13 | 14 |
| 30 m | 16 | 17 |
Where the length does not divide into whole bays, the last panel is cut down. Slotted concrete posts hold a cut panel easily; on timber posts, fix a vertical batten to the cut edge to stop the slats coming loose. Corners do not add posts, but each one needs a corner post rather than an intermediate one.
Add the panel height, the gravel board and the depth in the ground. The usual rule is 2ft (600 mm) in the ground, which suits most fences up to about 6ft. For a 6ft panel on a gravel board, which stands nearly 2 m high, the calculator buries the post 750 mm, as many suppliers do for extra resistance to wind.
| Panel | Gravel board | Fence height | Post to buy |
|---|---|---|---|
| 3ft | None | 0.91 m | 6ft (1.83 m) |
| 4ft | 150 mm | 1.37 m | 7ft (2.13 m) |
| 5ft | 300 mm | 1.82 m | 8ft (2.44 m) |
| 6ft | None | 1.83 m | 8ft (2.44 m) |
| 6ft | 150 mm | 1.98 m | 9ft (2.745 m) |
| 6ft | 300 mm | 2.13 m | 10ft (3.05 m) |
These match the usual merchant advice: 8ft posts for a 6ft panel on its own, or a 5ft panel on a 1ft gravel board, and 9ft posts for a 6ft panel with a gravel board.
On exposed sites, 6ft panels catch a lot of wind; concrete posts, deeper holes and panels with gaps, such as slatted designs, all help a fence survive storms.
A gravel board runs along the bottom of each bay, between the posts, so the panel is held clear of the soil. It stops the bottom of the panel rotting, protects it from strimmers and keeps the panel level where the ground slopes. A rotten gravel board is cheap to replace; a rotten panel is not.
Concrete gravel boards, usually 150 or 300 mm high, slot into concrete posts. Timber gravel boards are fixed to timber posts with small blocks of wood called cleats. Remember the board adds to the fence height and the post length: a 6ft panel on a 300 mm board makes a fence about 2.13 m high.
Postcrete is a ready-to-use, fast-setting concrete for posts. The Tarmac Blue Circle Postcrete data sheet gives these quantities for a 300 mm wide hole:
| Hole size (width × depth) | Bags per post |
|---|---|
| 300 × 450 mm | 1¾ |
| 300 × 600 mm | 2 |
| 300 × 750 mm | 2½ |
Fill the hole about a third full of water, stand the post in it, then pour the Postcrete evenly around the post until no water shows. It sets in about 10 minutes, so line up and plumb each post quickly. For a long fence, mixing your own concrete can be cheaper; our concrete calculator works out the volume.
A 15 m fence of 6ft panels on 150 mm concrete gravel boards, with slotted concrete posts:
For a fence with a low wall instead of gravel boards, our brick calculator works out the bricks and mortar, and for gravel along the base of the fence use our gravel calculator.
In England you can usually put up a fence without planning permission if it is no more than 2 m high, or 1 m high next to a road or a footpath beside a road used by vehicles. The height is measured from the ground, so it includes the gravel board. Listed buildings, conservation areas and some new estates have extra rules, so check with your council if in doubt. The Planning Portal explains the rules for walls, fences and gates.
Before you dig, check for buried pipes and cables, agree the line with your neighbour, and remember the finished side of the panels traditionally faces outwards, towards the neighbour.
With 100 mm posts, 6 panels and 7 posts: each bay of a 1.83 m panel plus a post takes about 1.93 m.
8ft (2.44 m) posts for 6ft panels on their own, or 9ft (2.745 m) posts if the panels sit on a gravel board, with 600 to 750 mm in the ground.
At least 600 mm (2ft) for most garden fences. For a 6ft panel on a gravel board, about 750 mm gives extra strength in the wind.
About 2 bags for a 300 mm wide hole 600 mm deep, and 2½ for a hole 750 mm deep, according to the Blue Circle Postcrete data sheet.
Standard panels are 6ft (1.83 m) wide, in heights from about 3ft to 6ft.
They are not essential but well worth it: they keep the panel off the soil so it lasts longer, and a damaged gravel board is cheap to replace.
Up to 2 m in England, or 1 m next to a road used by vehicles, measured from the ground and including any gravel board or trellis.
Concrete posts last longer and make replacing panels easy; timber posts are lighter, cheaper and easier to cut and fix.
Postcrete quantities from the Tarmac Blue Circle Postcrete product data sheet. Post lengths and slot types from UK concrete post suppliers. Planning limits from the permitted development rules for England. Reviewed November 2026.