How to use the fence calculator
- Choose boards / pickets for a fence built on site from posts, rails and boards (common in the US), or ready-made panels (common in the UK).
- Enter the total length, the distance between post centres (or the panel width) and the height.
- Add any gates — each one needs an extra post.
- Enter your post hole size to see how much concrete or post mix to buy.
How fence materials are calculated
Sections = fence length ÷ post spacing (rounded up) Posts = sections + 1 + gates Rails = sections × 2 (or × 3 if over about 4 ft / 1.25 m tall) Boards = fence length ÷ (board width + gap) Concrete = posts × (hole volume − post volume)
This assumes a straight run. Each corner or separate run starts a new line of posts, so add posts where your fence changes direction. Concrete bags assume a typical yield of about 0.6 ft³ per 80 lb bag.
Worked example (US)
A 100 ft privacy fence, 6 ft tall, with posts 8 ft apart: 13 sections, 14 posts, 39 rails (3 per section) and 219 boards at 5½ inches wide. With 10-inch holes 2 ft deep around 4 × 4 posts, you need about 22 × 80 lb bags of concrete.
Worked example (UK)
An 18.3 m run of 1.83 m panels: 10 panels and 11 posts. With 250 mm holes 600 mm deep around 100 mm posts, you need about 28 × 20 kg bags of post mix. Posts should be about 2.4 m long (1.8 m above ground plus 0.6 m buried).
Fence-building tips
- Check boundaries and rules first. Confirm where your property line is, and check local permits, HOA rules or planning limits on fence height.
- Call before you dig. In the US, call 811 to have buried utility lines marked. In the UK, check for cables and pipes before digging.
- Drainage: a few inches (50–100 mm) of gravel at the bottom of each hole helps stop posts rotting.
- Set the end posts first, run a string line between them, then set the posts in between.
Building a gravel path or concrete footings alongside? See the gravel calculator and concrete calculator.
Frequently asked questions
How many posts do I need for a 100 ft fence?
With posts every 8 ft, a straight 100 ft fence has 13 sections and needs 14 posts (one more post than sections). Add a post for each gate, and remember that corners and ends are always posts.
How deep should fence posts be?
A common rule is to bury about one third of the post’s total length, or at least half the above-ground height. For a 6 ft fence that means about 2 ft (600 mm for a 1.8 m UK fence). Go deeper in exposed, windy sites or loose soil, and below the frost line where ground freezes.
How many bags of concrete or postcrete per fence post?
It depends on the hole. A 10 inch × 2 ft hole around a 4 × 4 post takes about 1.5 × 80 lb bags. In the UK, a 250 mm × 600 mm hole around a 100 mm post takes about 2–3 × 20 kg bags of post mix. Narrower holes need less — the calculator works it out from your sizes.
What is the standard fence panel size in the UK?
Most UK fence panels are 6 ft (1.83 m) wide, in heights from 3 ft to 6 ft (0.9–1.8 m). With posts between them, post centres are slightly over 1.83 m — measure your chosen posts and panels.
How far apart should fence posts be?
In the US, posts are typically spaced 6–8 ft apart for wood privacy and picket fences. Panel fences are set by the panel width. Closer spacing makes a stronger fence in windy areas.