A straight fence is a row of bays. Each bay is one panel between two posts, and the posts are shared, so there is always one more post than panel.
Panels
Panels are the length of the run divided by the panel width, rounded up. Wickes lists overlap panels at 1.83 m wide. Bunnings lists wire panels at 2.4 m wide.
A 12 m run in 1.83 m panels is 6.56 panels, so 7. Seven panels cover 12.81 m, so the last one is cut or the run is adjusted.
| Run | UK panels | UK posts | UK bags | AU bays | AU posts | AU bags |
|---|---|---|---|---|---|---|
| 6 m | 4 | 5 | 10 | 3 | 4 | 8 |
| 10 m | 6 | 7 | 14 | 5 | 6 | 12 |
| 12 m | 7 | 8 | 16 | 5 | 6 | 12 |
| 15 m | 9 | 10 | 20 | 7 | 8 | 16 |
| 20 m | 11 | 12 | 24 | 9 | 10 | 20 |
| 30 m | 17 | 18 | 36 | 13 | 14 | 28 |
Posts, corners and gates
A straight run has one more post than panels. Corners and gates add posts; the calculator has an extra posts field for them.
Gravel boards sit under each panel, so there is one per bay.
Post mix
Two bags of fast-setting post mix per post is a common rule for a small timber post. The Blue Circle Postcrete data sheet gives 2 bags of 20 kg for a 100 mm post in a 300 mm by 600 mm hole, which is where the rule comes from.
A bigger hole, a bigger post or a square hole takes more. The Postcrete calculator works it out from the post and the hole.
Height and planning
The calculator does not take a height, so it is not a planning check. In England, permitted development rules (Part 2, Class A of the General Permitted Development Order) allow a fence up to 1 metre high next to a highway used by vehicles, or up to 2 metres elsewhere, without planning permission. Listed buildings, conservation areas and covenants can change that. Check GOV.UK or your council before you buy.
Figures are estimates for a shopping list. Check the pack or datasheet before you buy.