Calculate panels, posts, and postcrete bags for your fence
Planning a new fence is one of the most common garden projects in the UK, whether replacing storm-damaged panels or enclosing a new boundary. Getting the materials list right before you visit the builders' merchant saves time, money, and the frustration of a second trip. The key relationship in fence construction is the fence post problem: you always need one more post than the number of panels. A run of three panels needs four posts -- one at each end and one between each pair of panels. This simple but frequently overlooked rule is the most common source of error when ordering fence materials. Each fence post needs to be firmly set in the ground using postcrete (fast-setting post mix). The standard recommendation is two bags of 20kg postcrete per post, which provides a secure footing that sets in approximately 5-10 minutes when mixed with water in the hole.
To calculate fence materials: 1. Enter the total fence length in metres. Measure along the boundary line where the fence will be installed. If the fence changes direction (e.g. around a corner), measure each straight section separately and add them together. 2. Select the panel width. The UK standard is 1.83m (6ft), which is the most widely available and economical option. Shorter 1.52m (5ft) and 1.22m (4ft) panels are available for situations where a standard panel does not fit. 3. Review the results. The calculator shows the number of panels, posts (always one more than panels), and postcrete bags needed. The total length shows the actual fence length, which may be slightly longer than your measured boundary if the fence length is not an exact multiple of the panel width.
The fence calculation uses straightforward division with the critical fence post rule: Panels = ceil(fence length / panel width). For a 10m fence with 1.83m panels: ceil(10 / 1.83) = ceil(5.46) = 6 panels. Posts = panels + 1. This is the fence post principle: every panel needs a post on each side, and adjacent panels share posts. So 6 panels need 7 posts. Postcrete bags = posts x 2. Two bags of 20kg postcrete per post is the standard recommendation for a secure, long-lasting installation in most soil types. Total fence length = panels x panel width. Note this may exceed your measured boundary slightly because the number of panels is rounded up. In the example above, 6 x 1.83m = 10.98m -- just under a metre longer than the 10m boundary. The final panel can be cut to fit if needed.
Standard UK fence panel heights range from 0.9m (3ft) to 1.8m (6ft). Planning permission is generally not required for fences up to 2m high in rear gardens, or 1m high adjacent to a highway. Fence posts should be 75mm x 75mm (3" x 3") minimum for standard panels, set at least 600mm into the ground. In exposed or windy locations, consider concrete fence posts instead of timber, which do not rot and provide greater wind resistance.