How the planner works
Each straight side is worked out on its own. Then corner posts are shared and everything is added up. The difference between the two styles is where the posts go:
- UK style (panels between posts): a side with n panels is n × panel width + (n + 1) × post width long.
- US style (panels fixed to posts, one panel width apart): a side with n panels is n × panel width long.
panels per side = smallest whole number that reaches the side's length
posts = panels + 1 per side − shared corners
concrete per post = (hole area − post area) × hole depth
Worked examples
UK, one 10 m side: 1.83 m panels and 75 mm posts. 5 panels only reach 9.6 m, so you need 6 panels and 7 posts, with the last panel cut to about 0.32 m. In 300 × 600 mm holes that's 3 bags of 20 kg post-mix per post: 21 bags.
US, one 100 ft side: 8 ft panels on posts 8 ft on centre: 13 panels and 14 posts (the last panel is cut to 4 ft). In 10 in round holes, 24 in deep: 35 bags of 50 lb concrete mix.
The assumptions, in plain words
- Straight sides of panel fencing. Gates aren't included. Leave the gate gap out of your side lengths and add gate posts separately.
- Every cut panel is a full panel bought.
- Concrete fills the hole around a square post, and is rounded up to whole bags for the whole fence. Consider one spare bag.
- Post length = fence height + hole depth. Add more if your posts sit higher than the panels or on top of gravel boards.
Common mistakes to avoid
- Forgetting the posts take up room. In the UK style, every post adds its width to the run, which can mean one extra panel.
- Counting corner posts twice. Two sides that meet share one post.
- Buying posts that are too short. They need to go into the ground as well as up to the top of the fence.
- Mixing panel widths. Some UK panels are 1.80 m or 2.0 m wide, so check before you buy.
Measuring an awkward shape? See how to measure an irregular area.
Frequently asked questions
How many fence posts do I need?
One more than the number of panels on each straight side. Where two sides meet at a corner, they share a post. A fence that goes all the way round (a closed loop) shares one more. The planner does this counting for you.
How far apart are fence posts?
In the UK, panels usually sit between the posts, so the posts are one panel width plus one post width apart: about 1.905 m for 1.83 m panels and 75 mm posts. US pre-built panels are commonly 8 ft wide and fixed to posts set 8 ft on centre. Always check the panel you are buying.
What if my fence length is not an exact number of panels?
The last panel on that side has to be cut down. The planner tells you which side needs a cut panel and how wide it ends up. You still buy a full panel for it.
How long should fence posts be?
At least the fence height plus the depth of the hole. The planner works this out. Round up to the next post length your supplier sells.
How many bags of post-mix per post?
It depends on the hole size. For a 75 mm post in a 300 × 600 mm hole, a supplier’s table gives 3 bags of 20 kg post-mix. The planner uses your hole size and bag, and rounds up for the whole fence.
Sources
Last updated 11 November 2026. Found a mistake? Tell us.