Measuring up for a fence seems straightforward until you're standing in the garden realising you ordered 8 panels and you need 11. Or you've got two panels left over and nowhere to return them. Accurate fencing calculations prevent both scenarios — and they're not complicated once you know the method.
Step 1: Measure the Total Linear Length
Walk the perimeter of the area to be fenced and measure each straight run separately. Don't try to measure the whole perimeter in one go around corners — measure each side individually and add them up. For curved boundaries, use a piece of string laid along the curve, then measure the string.
Record all measurements in metres. Our area and measurement calculator can help you keep track of multiple measurements. For the associated groundwork, our concrete calculator works out post footing volumes.
Step 2: Subtract Gate Openings
Measure any gate openings and subtract them from the total run — you don't need fencing panels there. Standard gate widths: pedestrian gate 900mm-1.2m, single vehicle gate 3-3.6m, double vehicle gate 4.5-5m. Always measure the actual opening you need, not a standard size.
Step 3: Calculate Number of Panels
Standard fence panels are typically 1.83m (6ft) wide, though 1.2m and 2.4m panels are also available. Divide your total run (in metres, after subtracting gates) by the panel width: Total panels = Total run ÷ Panel width. Round up to the nearest whole number.
Example: 27m total run, 3m of gates, 1.83m panels: (27 − 3) ÷ 1.83 = 13.1 → order 14 panels.
Step 4: Calculate Posts
You need one post at each end and one between every pair of panels. Posts = number of panels + 1. For 14 panels: 15 posts. For corner and intermediate posts along a straight run, this formula applies. Gate posts are usually heavier gauge and ordered separately.
Post Depth and Concrete
Posts should be buried to at least a third of their total length — a 1.8m panel needs a 2.4m post (600mm in ground). In clay or wet soil, go deeper. For a standard concrete mix footing around each post: typically 10-15 litres per post hole (roughly 20kg bag of postcrete per post). Multiply post count by 20kg bags for your concrete order.
Sloping Ground
On slopes you have two options: step the fence (panels are horizontal, each stepped down the slope) or rake the fence (panels follow the slope at an angle). Stepped fencing is simpler and uses standard panels. Raked fencing requires custom panels or gravel boards cut to angle. Measure slope runs individually — the panel count stays the same but the post heights vary for stepped fencing.
Gravel Boards
Gravel boards sit at the base of the fence between posts, keeping wooden panels off damp ground and extending panel life significantly. Calculate one gravel board per panel bay — same count as your panels.
Further reading: The Planning Portal provides guidance on when garden fences require planning permission. Check fence planning permission requirements at the Planning Portal.