Fence Post Spacing Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
The number of posts is calculated by dividing the fence's length by the recommended spacing, then adding 1 (a post at each end). For 20 m of wood fencing spaced 2 m apart, 11 posts are needed.
Explanation
Calculating the number of fence posts is a classic instance of the "poles and intervals" problem: over a given length, the number of gaps between posts is the length divided by the spacing, but the number of posts is always that number of gaps plus one, since a post is needed at each end in addition to the intermediate posts — a common pitfall that systematically underestimates the real number of posts needed by one. The recommended spacing varies by fence type: about 2 m for wood posts on flat ground, 2.5 m for flexible or rigid wire mesh (the most commonly cited standard spacing), and up to 3 m for an agricultural fence on stable ground. On sloped, uneven, or wind-exposed ground, it's recommended to reduce this spacing to strengthen the overall stability, even if that means more posts than the basic calculation indicates. This calculation pairs well with our stud spacing calculator, which addresses the same math problem for a cladding or drywall frame rather than an outdoor fence, or with our garden fertilizer dosage calculator for the rest of the outdoor landscaping.
Example for a 20 m wood fence
Inputs
Length: 20 m. Type: wood posts (2 m spacing).
Calculation
Number of posts = (20 ÷ 2) + 1 = 10 + 1 = 11.
Result
A 20 m wood fence spaced 2 m apart needs 11 posts.
Frequently asked questions
Why add 1 to the division result?
Because a post is needed at each end of the fence, in addition to the intermediate posts marking each gap. A fence with 3 gaps always has 4 posts, never 3 — the classic mistake is forgetting this extra post.
Should spacing be reduced on sloped ground?
Yes, sloped, uneven, or very wind-exposed ground weakens the fence's stability: reducing the spacing (for example to 1.5-2 m instead of 2.5 m for wire mesh) strengthens the structure, at the cost of extra posts.
Does this calculation apply to a plot with corners?
This calculation assumes a straight line. For a plot with corners, calculate each segment separately, counting one corner post for each change of direction — that post counts for both segments it connects, not twice.