How the Gravel Board Calculator Works

Enter your fence length and the bay width your posts are set at. The calculator divides the run into bays and returns one gravel board per bay, with the board length matched to your system: 1.83m (6ft) boards for standard panel fencing, and 3m lengths where closeboard runs on wider traditional bays.

The counting rule is simple because gravel boards mirror the panels: a 20-metre run of standard 6ft panel fencing has 11 bays, so it needs 11 gravel boards, sitting in the same slotted posts or fixed to the same timber posts as the panels above them. If you are calculating the actual posts and panels needed for the entire boundary, use our dedicated Fence Panel Calculator or look at post concrete using our Fence Post Concrete Calculator.

What Gravel Boards Actually Do

A gravel board is a sacrificial barrier between the ground and the fence. Timber in contact with the soil stays damp, and damp timber rots. This is why unprotected fence panels fail from the bottom edge years before the rest of the board weathers. The gravel board takes that ground contact instead, lifting the panel 150mm or more clear of soil, splash, and standing water.

The economics are the whole argument: a £10 to £20 board protects a £40 to £70 panel and can extend its life by 5 to 10 years. When the gravel board itself eventually decays, it swaps out in minutes for a fraction of a panel's price. Fences built without them are choosing to replace panels early.

Concrete or Timber Boards

The material choice follows your posts. Concrete gravel boards, in 150mm and 300mm heights, never rot, slot straight into concrete posts, and are the default for panel systems—with the practical note that they only work with slotted concrete posts since timber posts have nothing to hold them. Timber gravel boards, typically 150 × 22mm treated boards, suit closeboard fences on timber posts, screwed to cleats or the posts themselves. They cost less but will eventually need replacing.

The 300mm concrete board earns its place in two situations: where soil sits higher on one side of the boundary than the other, and where extra fence height is wanted without taller panels, since the board adds its height to the total. On that point, remember the planning limit: the fence plus the gravel board together must stay within 2 metres in most gardens, so a 1.8m panel on a 300mm board technically breaches it, while a 1.65m panel on a 300mm board sits neatly at 1.95m.

One wildlife kindness worth building in: hedgehog-friendly gravel boards with a 13cm gap (or simply leaving a gap under one board) keep garden corridors open for a species that has lost most of its habitat connectivity.

Worked Example

A 27.5-metre boundary in 6ft panels on slotted concrete posts, with one side of the garden sitting 200mm higher than the neighbour's:

• Bays: 27.5 ÷ 1.83 = 15 bays
• Standard runs: 12 × 150mm concrete gravel boards
• Raised soil section: 3 × 300mm concrete boards to retain the higher ground
• Panel heights: Panel heights adjusted so the board plus panel stays under 2m throughout.

Mixing board heights along a run like this is routine, and pricing taller boards only where the ground demands them keeps the cost sensible.