My fence project went slightly over budget because my initial planning involved one measurement error that then rippled through the entire material order.
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.
Measuring Your Fence Line Accurately
Walk the boundary and note every change of direction — corners, gates, existing structures the fence must connect to or stop at. Measure each straight section separately with a tape measure. For long sections, use a surveyor's tape rather than a standard tape measure, as extending a short tape multiple times accumulates errors. Add the section measurements together for total fence length. For post spacing, divide the total length by your chosen panel width (typically 1.8m or 1.83m for standard fencing panels) to find the number of panels, then add 1 for the number of posts required at each end and corner.
What to Order Beyond Panels and Posts
Each post requires either a concrete post spike (for soft or medium ground) or a concrete footing. For a standard 1.8m panel fence using 75mm square timber posts, each concrete footing is typically 300mm × 300mm × 600mm deep — roughly 0.054 m³ of concrete per post. Multiply by the number of posts to get your concrete requirement. Gravel boards are used below panels to protect the base from ground contact — these are measured by the same linear run as the panels. Arris rails (cross-members) are needed if building a post and rail fence rather than a panel fence.
Gate Gaps and Openings
Subtract gate widths from your total fence run before calculating panels. A standard single gate is 900mm wide; a double gate is typically 1.8m. Allow 10mm each side of the gate for clearance within the frame. Gate posts are heavier duty than fence posts — typically 100mm × 100mm for a garden gate — and need deeper, larger footings because they carry the weight and movement of the gate. If installing both a fence and gates, note the gate post requirements separately as they require different materials and more substantial concrete.
Avoiding Common Ordering Mistakes
Ordering panels in the exact calculated count means running short if any panel needs to be cut to fit an awkward length, or if one arrives damaged. Order one or two additional panels as a buffer. Posts, gravel boards, and post caps are sold separately and are easy to forget. Make a complete materials list before placing your order: panels, posts, gravel boards, post caps, concrete or post spikes, coach screws or panel clips, and any preservative if using untreated timber.