Enter the total length of fence, the panel width and the post thickness. The calculator counts panels, posts, gravel boards, bags of post-mix and gates, and adds up a cost if you enter prices.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the Fencing calculator works
Each bay is one panel plus one post. For a run of length L with gates taking up total width G, the usable length is L − G. With panel width w and post thickness p, the number of panels is:
ceil((L − G − p) ÷ (w + p))
- Posts: an open run needs one more post than panels. A closed boundary has the same number of posts as panels. Each gate adds one post.
- Gravel boards: one under each panel if you choose that.
- Post-mix: posts × bags per post, rounded up.
- Corner posts are counted among the total, not added to it.
- Cost is the quantities multiplied by the prices you enter.
The tool also shows the spare length, because the last panel is usually cut. It treats the run as one straight line, so for a fence with several sides, measure each side to see exactly where the cut panels fall.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Measurements in | Metres |
| Total run of fence | 20 |
| Layout | Open run with two ends |
| Panel width | 1.83 |
| Post thickness | 10 cm |
| Corner posts | 0 |
| Gates | 1 |
| Gate opening | 0.9 |
| Gravel boards | One under each panel |
| Bags of post-mix per post | 2 |
| Price per panel (optional) | £35 |
| Price per post (optional) | £12 |
| Price per gravel board (optional) | £9 |
| Price per bag of post-mix (optional) | £6 |
| Price per gate (optional) | £90 |
Panels needed: 10 panels and 12 posts
| Fence length excluding gates | 19.1 m |
|---|---|
| Panels | 10 |
| Posts in total | 12 |
| Of which end posts | 2 |
| Of which corner posts | 0 |
| Of which gate posts | 1 |
Tips and common mistakes
Measure along the line of the fence, not across the garden, and mark post positions with string before you buy. Slopes need stepped panels or raked cuts, which can use more panels. Check the post length: it should be the panel height plus the depth in the ground, usually about a third of the height below ground. Confirm the neighbour’s boundary and any permission or height limits with your council before you build.
Frequently asked questions
How many posts do I need for a fence?
An open run needs one more post than panels, because both ends need a post. A closed boundary needs the same number of posts as panels. Each gate adds one extra post.
How many bags of post-mix per post?
It depends on the hole size and post size. A common starting point is about two bags per post, but check the instructions on the bag.
What if my run is not a whole number of panels?
The last panel is cut to fit, or you can space the posts slightly wider. The calculator shows the spare length so you can decide.