Home & Construction⏱ 4 min read
How to Calculate How Many Fence Panels and Posts You Need
Fencing seems simple until you start ordering materials and realise you've forgotten about end posts, corner posts, and the gap at the gate. Here's the complete formula.
Fencing calculations trip up even experienced DIYers because the relationship between panels and posts isn't obvious, and gates and corners add complications. Here's the complete method.
The Basic Formula
Panels = Total run length ÷ Panel width (round down)
Posts = Panels + 1
Standard panel width: 1.83m (6ft)
Standard post spacing: 1.83m centre-to-centre
Example: 18.3m fence run
Panels = 18.3 ÷ 1.83 = 10 panels
Posts = 10 + 1 = 11 posts
The posts + 1 rule holds for a straight run: every section between two posts is a panel, and you always need one more post than panels to close the run.
Corners and Gates
Corner post: adds 1 post but doesn't reduce panels
Gate opening: removes 1 panel, adds 2 posts (gate posts)
Example: L-shaped garden with a gate
Side A: 12.2m = 6 panels + 7 posts
Corner: +1 post (shared with Side B)
Side B: 9.15m = 5 panels + 6 posts
Less corner already counted: −1 post
Gate: −1 panel, +2 gate posts
Total panels: 11 − 1 = 10 panels
Total posts: 7 + 1 + 6 − 1 + 2 = 15 posts
Partial Panels at the End
If your run doesn't divide evenly by panel width, you'll have a gap at the end. Options:
- Order one extra panel and cut it to fit (most common)
- Adjust post spacing slightly along the run to avoid a narrow offcut
- Use a different-width panel for the final section (some ranges offer 0.91m / 3ft panels)
Example: 20m run, 1.83m panels
20 ÷ 1.83 = 10.93 → 10 full panels + 0.93m gap
= 10 full panels + 1 cut panel (cut to 0.93m)
Posts: 12
Post Depth and Length
Post length = Panel height + Post depth in ground
Rule: post depth = 1/3 of total post length (minimum)
Or: fence height ÷ 2 (for exposed sites / tall fences)
Standard 1.83m (6ft) panel:
Post depth: 0.6m minimum (ideally 0.75m)
Post length: 1.83 + 0.6 = 2.43m → buy 2.4m posts
Post depth also depends on soil:
Clay: 0.5m minimum
Sandy / loose soil: 0.75m+
Gravel Boards
Gravel boards sit at the base of panels, raising them off the ground to prevent rot. Standard size: 150mm × 1.83m. If using gravel boards, add 150mm to your post length calculation:
With gravel board: post length = panel height + gravel board height + post depth
= 1.83 + 0.15 + 0.6 = 2.58m → buy 2.7m posts
Quantity Summary Table
ItemCalculationAdd 10% wastage?
PanelsRun ÷ panel width (round up)No — exact count
PostsPanels + 1 + corners + gate postsOrder 1 spare
Gravel boardsSame count as panelsNo
Post mix / concrete2 bags per post (25kg bags)Order 1 extra bag
Post caps1 per postNo