How the fence calculator works
Standard UK fence panels are 1.83m (6ft) wide. With a post between each panel, every bay is about 1.93m. The calculator divides each straight run into bays, adds one post per panel plus an end post for each run, and picks the right post length for your panel height:
Post length guide
| Panel height | Post length | In the ground |
|---|---|---|
| 0.9m (3ft) | 1.5m | ~450–600mm |
| 1.2m (4ft) | 1.8m | ~600mm |
| 1.5m (5ft) | 2.1m | ~600mm |
| 1.8m (6ft) | 2.4m | ~600mm (with gravel board) |
Fence building tips
- Check boundaries and talk to your neighbours first. In England, fences over 2m high (1m next to a highway) need planning permission.
- Run a string line along the fence and dig holes about 300mm wide and 600mm deep.
- Fit gravel boards so panels sit clear of the soil. Rotten panel bottoms are the main reason fences fail.
- Set the first post, fix the panel, then set the next post. Don't concrete all the posts in first.
Worked example: a 20m back fence
A straight 20m run of 1.8m (6ft) panels with 100mm timber posts: each bay is 1.83m + 0.1m = 1.93m, and 20 ÷ 1.93 = 10.4, so 11 panels. One run needs one more post than panels: 12 posts of 2.4m. With gravel boards that's 11 boards, and at two 20kg bags per post, 24 bags of Postcrete. Timber panels also need four clips each, 44 in total.
If the same 20m goes round three sides of a garden (5m, 10m and 5m), each side has its own end posts and usually a cut panel, so it comes to about 13 panels and 15 posts. Set "Separate straight runs" to 3 to see this.
Timber or concrete posts?
- Timber posts (100 × 100mm, pressure treated) are cheaper, lighter and easy to cut. Panels are fixed with clips. Expect them to last 10–15 years with good drainage at the base.
- Concrete slotted posts cost more and are heavy, but they don't rot. Panels slide into the slots, so a storm-damaged panel can be swapped without disturbing the posts. Use concrete gravel boards with them.
- In exposed, windy gardens, closeboard or slatted fences resist wind better than solid lap panels, which act like a sail.
Sloping gardens
Panels can't follow a slope; they're stepped. Each panel sits level, and the posts get taller down the hill. On a steep slope you'll need longer posts at the low end, and a triangle of gravel board or brickwork to fill the gap underneath. Work out the drop over the run before ordering, so you know how many longer posts to buy.
Common fencing mistakes
- Shallow posts. Less than about 600mm in the ground for a 6ft fence is the most common reason fences blow over.
- Panels touching the soil. Timber in contact with damp ground rots quickly. Gravel boards are cheap protection.
- Not agreeing the boundary. Check your title plan and talk to the neighbours before you start. Our fence guide explains who usually owns which fence and what to do after storm damage.
To plan the whole job, including a skip for the old fence and a gravel border, use the new fence planner. For posts set in mixed concrete rather than Postcrete, the concrete calculator has a post-hole option.