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Fence calculator: posts, concrete, rails, and pickets
Estimate how many posts you need for a fence line, the concrete to anchor them, the horizontal rails, and the boards or pickets based on their width. Works in metric or US units, with adjustable post spacing and hole dimensions.
Last reviewed: September 2026 · How we calculate
Input data
Add the board width plus the gap between boards.
Results
Enter your data and press Calculate.
Results are estimates. Always check the manufacturer's or supplier's specifications before buying.
Unit converter
How a fence is calculated
A fence breaks down into four line items: posts (one every set spacing, plus one extra at the end), concrete to anchor each post in its hole, horizontal rails running between posts, and boards or pickets covering the total length based on their width. This calculator solves all four at once from the total length and post spacing.
Formula
Hole volume = π × (Diameter ÷ 2)² × Depth
Total concrete = Posts × Hole volume × (1 + Waste ÷ 100)
Rails = (Posts − 1) × Rails per section
Boards/pickets = ⌈Length ÷ (Board width + gap)⌉
Worked example
A 20 m (66 ft) fence, posts every 2.4 m (8 ft), holes 30 cm (12 in) diameter × 60 cm (24 in) deep, 2 rails per section, and 16 cm boards (gap included) — the calculator's defaults:
| Posts | ⌈20 ÷ 2.4⌉ + 1 = 9 + 1 = 10 posts |
|---|---|
| Volume per hole | π × 0.15² × 0.6 ≈ 0.0424 m³ |
| Total concrete (5% waste) | 10 × 0.0424 × 1.05 ≈ 0.445 m³ → 20 bags of 50 kg |
| Rails | (10 − 1) × 2 = 18 rails |
| Boards/pickets | ⌈20 ÷ 0.16⌉ = 125 pieces |
Check these numbers by pressing "Calculate" with the default values: the calculator automatically converts concrete to 50 kg bags (0.0225 m³ per bag, the same yield used by the concrete calculator).
Hole depth: the one-third rule
A widely used rule of thumb is to bury the post one third of its total height above ground (for example, a post with 1.8 m / 6 ft showing needs ~60 cm / 24 in of hole). In windy areas, tall fences, or loose soil, go deeper. Hole diameter is usually 3 times the post width, leaving room for concrete to fully surround it.
Post spacing: why 2.4 m (8 ft) is the standard
2.4 m (8 ft) is the most common spacing because it matches the standard length of commercial boards, panels, and rails, minimizing cuts and waste. For mesh or wire fencing, spacing can go up to 3 m (10 ft); for block walls or rigid panels, shorten it to 2–2.4 m (6.5–8 ft) for more structural support.
Common mistakes when calculating a fence
- Forgetting the extra end post. If the line is 20 m with posts every 2.4 m, you need 9 sections but 10 posts (one at each end of every section).
- Not digging the hole deep enough. A shallow hole lets the fence lean over time, especially in soft soil or windy areas.
- Calculating boards without adding the gap between them. The width to use is the board PLUS the ventilation gap between boards, not just the board width.
- Not allowing for corner waste. Corners and end runs almost always generate extra cuts; a 5–10% margin covers them.
Frequently asked questions
Why does the calculator add an extra post?
Because the number of posts is always one more than the number of sections: a 3-section fence needs 4 posts (one at each end of every section, sharing the posts in between).
What hole depth should I use?
A practical reference is one third of the post's visible height. For standard residential fence posts (1.5–1.8 m / 5–6 ft), 45–60 cm (18–24 in) of depth is usually enough; in windy areas, go deeper.
Does the calculator include mesh or panels?
Not directly — it calculates posts, concrete, rails, and boards/pickets. If you're using mesh or prefab panels, count rolls or panels based on total length and each piece's width.
How do I choose the post spacing?
2.4 m (8 ft) is the standard because it matches the commercial length of boards and panels. For heavier fencing (block, rigid panels) reduce to 2 m (6.5 ft); for mesh or wire you can go up to 3 m (10 ft).
Is concrete calculated the same as in the concrete calculator?
Yes. It uses the same 0.0225 m³ per 50 kg bag yield, so results are consistent between both calculators.