How many fence posts do I need? Posts, bays, mesh, panels and concrete

Short answer: number of bays = fence length ÷ maximum post spacing, rounded up, and a straight open run has one more post than bays. For 30 m of fence with posts at most 2.5 m apart that is 30 ÷ 2.5 = 12 bays and 13 posts. Corners, gates, panels and sloping ground change the number and type of posts – here is how, with illustrative examples calculated by the fence calculator.

Formula for a straight fence

Bays = ⌈length ÷ spacing⌉, posts = bays + 1. The calculator then splits the run into equal bays no wider than the set spacing. Example A: a 30 m mesh fence, 1.5 m high, spacing at most 2.5 m gives 12 bays of 2.5 m and 13 posts – 2 end posts, 1 straining post (added every 25 m of mesh) and 10 line posts. Mesh: 30 m + 5 % reserve = 31.5 m, so 2 rolls of 25 m.

Corners and a fence around the whole plot

At a corner two sides share one post, so it is counted once. Each side is split separately because a post must stand at every corner. Example B: a 25 × 16 m yard (perimeter 82 m), spacing up to 2.5 m: 25 m gives 10 bays, 16 m gives 7 bays, 34 bays and 34 posts in total. A closed fence has no end posts, so it has as many posts as bays.

Gates and openings

Gates interrupt the infill and get their own posts with a heavier section and a bigger footing. The same yard with a 3 m driveway gate and a 1 m pedestrian opening at the front: the calculator counts 35 posts (4 corner, 4 gate posts and 27 line posts) and 33 bays. Mesh is counted only on the 78 m of fence without openings: 4 rolls of 25 m.

Panel fence

With panels the spacing is fixed: post centres = panel width + post width. Example C: 20 m of fence, 2.5 m panels and 6 cm posts: 20 ÷ 2.56 = 7.8, so 7 full panels and 1 shortened (cut) panel, 8 bays and 9 posts in total.

Sloping ground

On a slope panels and mesh are usually stepped: bays stay level and the posts must be longer by the step height. Example D: 20 m of mesh with a 1.2 m level difference gives 8 bays of 2.5 m and a step of 1.2 × 2.5 ÷ 20 = 0.15 m, so the posts are 1.5 + 0.6 + 0.15 = 2.25 m long instead of 2.1 m.

Concrete for post footings

For a line post the calculator uses a 25 × 25 × 50 cm footing, and 30 × 30 × 60 cm for end, corner, straining and gate posts, minus the part of the post in the concrete (0.6 m embedment, round post Ø 6 cm). That is 29.8 L per line post and 52.3 L per heavy post, plus a 5 % reserve. These are calculator defaults, not a structural design: footing sizes come from the system manufacturer or a designer.

Example	Bays	Posts	Concrete (m³)
A: straight mesh 30 m	12	13	0.48
B: 25 × 16 m yard with gates	33	35	1.29
C: panels 20 m	8	9	0.33
D: mesh 20 m on a slope	8	9	0.33

Common mistakes

Length ÷ spacing without adding the last post (the classic “fencepost error”).
One formula for the whole perimeter instead of each side separately – the corner then gets no post.
Forgotten gate and opening posts and their heavier footing.
A panel fence calculated like mesh, without the post width in the spacing.
Posts on a slope as long as on level ground.

Sources and assumptions

The examples are illustrative calculations with this app’s fence calculator function (default spacing, embedment, footings and reserves); load-bearing capacity and wind resistance are not checked.

Wikipedia: Off-by-one error – fencepost error

Frequently asked questions

How many posts for a 50 m fence?

With spacing up to 2.5 m: 20 bays and 21 posts in a straight run, including 1 straining post for mesh. Corners can add a bay because each side is split separately, and gates add gate posts.

How far apart should fence posts be?

For mesh and timber the calculator uses at most 2.5 m; for panels the post centres are panel width + post width (e.g. 2.5 m + 6 cm). Take the exact value from the system manufacturer’s instructions.

How much concrete per fence post?

With the calculator’s default footings about 29.8 L for a line post and about 52.3 L for an end, corner, straining or gate post, before the 5 % reserve.

Open the calculator: Fence calculator