How Many Fence Panels and Posts Do I Need?

Everything in fencing is counted in bays — the run between one post and the next. A standard UK fence panel is 1.83 m (6 ft) wide, and once you add a post you get a bay pitch of roughly 1.93 m centre to centre. So the number of panels is your total run divided by 1.93, rounded up. A 20 m fence is 20 ÷ 1.93 = 10.36, which rounds to 11 panels. Simple enough, but the rounding always goes up, never down, because you can trim a panel to fit but you can't stretch one. Takeaway: divide your run by 1.93 m and round up — that's your panel count, and it's always a round-up.

Here's the rule people get wrong. You do not have one post per panel. Every run needs a post at both ends, so the number of posts is always the number of panels plus one. Eleven panels means twelve posts. On a short three-panel run it's four posts. It sounds obvious written down, but it's the single most common reason a delivery comes up one post short, because it's easy to order eleven of everything and forget the fence has two ends. If your fence returns around a corner or has a gate, each of those adds a post too. Takeaway: posts = panels + 1, before you add any extra for corners and gates.

Gravel boards, the strip that sits along the bottom of each bay to keep the timber off wet soil, work out at one per bay — so they match your panel count. Eleven panels, eleven gravel boards. They're the cheapest single thing you can do to make a fence last, because ground-level rot is what kills most timber fences first.

Then there's the postmix, which is the line that quietly doubles on a taller fence. As a rule, budget one 20 kg bag per post for fences up to 1.2 m, and two bags per post above that — which is where most domestic 1.8 m fences land. Twelve posts on a 1.8 m fence is therefore around 24 bags of postmix, not twelve. It's a genuine cost and a genuinely heavy thing to carry, so it's worth getting right before you're at the merchant. Takeaway: gravel boards match panels; postmix is one bag per post up to 1.2 m and two bags per post above it.

A common mistake is buying posts the same height as the fence. You need roughly a quarter to a third of the post in the ground for stability, so a 1.8 m fence takes a 2.4 m post, with about 600 mm concreted below ground. Skimp on the buried depth and the first proper gale will lean the whole run. Concrete posts for a 1.8 m fence are typically 2.4 m long; timber posts are usually 100 × 100 mm and the same length. Takeaway: buy posts around 600 mm longer than the fence height so there's enough in the ground — a 1.8 m fence needs 2.4 m posts.

Take a 20 m back-garden boundary in Leeds at 1.8 m high, using overlap panels with concrete posts and concrete gravel boards.

The counts above assume pre-made panels. If you're building closeboard (featheredge) instead — vertical boards nailed to horizontal arris rails on site — the panel count disappears and you count boards. A featheredge board about 125 mm wide with a 25 mm overlap covers roughly 100 mm of run, so a 1.8 m bay swallows around 18 boards, and a 20 m run is getting on for 200 boards plus rails. Closeboard uses far more parts and takes much longer, which is why it costs more even though the raw timber looks cheap per piece. It also lasts longer and repairs board by board, which panels don't. Takeaway: closeboard is counted in boards, not panels — roughly 18 boards a bay — and needs far more parts than a panel fence.

Most guides tell you to mark out your posts at a neat 1.93 m grid and set them all. Ask anyone who fits fences for a living and they'll tell you the opposite. Timber panels vary by a few millimetres from batch to batch, and ground is never as level as a plan. The reliable method is to set the two end posts first against a string line, then set each intermediate post to the panel you're actually holding, not to a theoretical measurement. Fit a panel, mark the next post off it, dig, set, repeat. Force real panels onto a paper grid and you'll be cutting the last one down to fit an awkward gap. Takeaway: set your ends first, then let each post follow the actual panel in your hands — don't build to the drawing.

The rules above get you close, but corners, gates and a mix of panel heights change the count quickly. The Fencing Cost Calculator UK works out panels, posts, gravel boards and postmix for your run and gives you a materials total and cost per metre. If you're setting posts in concrete, the Concrete Volume Calculator helps with larger post holes, and once the fence is up the Gravel Calculator UK and Decking Area Calculator cover the rest of the garden.