Fence Post Spacing Calculator
Number of posts
18
How it works
Calculating fence post spacing and the number of posts needed seems straightforward but involves a non-obvious consideration: the span between posts must be consistent while the fence must terminate exactly at the end points. Naïve division may leave a partial panel at the end. The Fence Post Spacing Calculator distributes posts evenly while minimising end-panel waste.
**Basic calculation** For a fence run of total length L with panel width P: Number of panels = ceil(L / P). Post count = panels + 1 (for a straight run). Corner posts, gate posts, and end posts count as standard posts.
**Example** 30m fence run with 1.8m panels: 30 / 1.8 = 16.67 → 17 panels needed. 17 panels × 1.8m = 30.6m (0.6m overshoot). To fit exactly: either cut the last panel to 30 − 16 × 1.8 = 1.2m, or distribute the 0.6m excess across all spans (30/17 ≈ 1.765m per panel — barely noticeable and stronger than a short end panel).
**Post hole depth** Standard rule: post hole depth = 1/3 to 1/2 of the above-ground post height. For a 1.8m fence (posts need ~0.6m above ground): set in 600mm deep holes. In frost-prone areas, holes must go below frost depth (varies by region: 400mm in southern UK; 600–900mm in northern Canada). Footings in concrete: mix one 20kg bag per 150mm × 150mm hole.
**Post size recommendations** 75mm × 75mm posts: adequate for up to 1.2m fence height. 100mm × 100mm: standard for 1.5–1.8m fences. 125mm × 125mm: required for 2.4m privacy fences and gates with significant wind exposure.
Privacy: all calculations run in the browser. No data is transmitted.
Frequently Asked Questions
- The standard depth rule: posts should be set in the ground at least 1/3 of their total length. For a 1.8m (6ft) fence: posts are typically 2.4m (8ft) long, with 600mm (2ft) in the ground. In loose/sandy soil or areas with high wind exposure: increase to 1/2 the post length (900mm for an 8ft post). In frost-prone areas: footings must extend below the frost depth — 400–600mm in the UK, 900–1200mm in cold parts of North America. Concrete footings around posts add significantly to lateral stability but must be sloped at the top surface to drain water away from the post (prevents rot at the critical rot zone).
- Maximum spans depend on fence height and wind exposure: standard 1.8m (6ft) privacy fence: 2.4m (8ft) maximum post spacing. Picket fence (1.2m): 2.4–3.0m spans are acceptable. Close-board fence in exposed locations: 1.8m or even 1.5m spans recommended. Reducing post spacing increases stability, especially for tall privacy fencing which presents a large wind load surface. Gate posts should always be set more securely (deeper, wider concrete footings) than standard fence posts — gate weight and repeated swing loading stress the posts significantly.
- Two approaches: stepped fencing — keeps fence panels horizontal but creates gaps under panels where the ground drops. Suitable for privacy fences where gaps are filled with gravel boards. Raked/sloped fencing — panels are angled to follow the ground slope. Works well for picket-style fences; more difficult with close-board panels. For significant grade changes (>200mm over a panel span), step fencing is simpler and provides better structural integrity. Each step starts a new level section — measure the drop between post positions and adjust post heights to keep panels level at each step.
- A gravel board is a horizontal timber board (typically 22mm × 150mm) fixed at the base of a fence, between the ground and the bottom rail/panel. It serves two purposes: (1) Keeps the main fence boards off the ground — ground contact causes rapid rot even in pressure-treated timber. The gravel board is in contact with the ground and can be replaced cheaply when it rots, extending the life of the main fence panels significantly. (2) Fills the gap between ground and fence bottom for privacy. In stepped fencing where ground slopes, longer gravel boards or adjustable base sections fill the varying gap at each step.