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Fence Calculator

Estimates the posts, rails and pickets for a straight run of wooden fence from the total length, the maximum post spacing, the number and width of gates, the rails per section and the picket width plus gap.

Unit system (optional)Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems. Total fence length (m or ft)Overall length of the fence line including gate openings (m or ft). Maximum post spacing (m or ft) (optional)Maximum centre-to-centre distance between posts; sections are spaced evenly at or below this. Default 2.4 m (metric) or 8 ft (imperial). Gates (optional)Number of gate openings in the run; each takes a bay between two posts. Gate width (m or ft) (optional)Width of each gate opening. Default 1 m (metric) or 3 ft (imperial). Rails per section (optional)Horizontal rails between each pair of posts: 2 for fences up to about 1.2 m / 4 ft, 3 for 1.8 m / 6 ft privacy fences. Picket width (mm or in) (optional)Width of one picket/board in millimetres (metric) or inches (imperial). Optional; enables the picket count. Gap between pickets (mm or in) (optional)Gap between pickets (0 for a solid privacy fence), in mm or in.

When to use

You need a material list (posts, rails, pickets) for a picket, privacy or post-and-rail fence of a known length.

Do not use when: You need concrete for the post holes (use cylinder for the hole volume and concrete-slab for bags), or the fence is chain-link or panel fencing sold per panel (divide the length by the panel width instead).

Formula

fence_length = total_length − gates × gate_width; sections = ceil(fence_length / post_spacing); posts = sections + gates + 1; actual_spacing = fence_length / sections; rails = sections × rails_per_section; pickets = ceil(fence_length / (picket_width + picket_gap)).

Assumes one straight run with posts at both ends and gates as extra bays; for a closed loop (fence all the way round) subtract 1 post, and add one post per corner or change of direction. Gate hardware, post concrete and cap rails are not included.

Inputs

Parameter	Type	Unit	Required	Description
`unit_system`	enum: metric \| imperial		default metric	Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems.
`total_length`	number	m or ft	yes	Overall length of the fence line including gate openings (m or ft). Range: > 0, ≤ 100000
`post_spacing`	number	m or ft	no	Maximum centre-to-centre distance between posts; sections are spaced evenly at or below this. Default 2.4 m (metric) or 8 ft (imperial). Range: > 0, ≤ 20
`gates`	integer		default 0	Number of gate openings in the run; each takes a bay between two posts. Range: ≥ 0, ≤ 50
`gate_width`	number	m or ft	no	Width of each gate opening. Default 1 m (metric) or 3 ft (imperial). Range: > 0, ≤ 10
`rails_per_section`	integer		default 2	Horizontal rails between each pair of posts: 2 for fences up to about 1.2 m / 4 ft, 3 for 1.8 m / 6 ft privacy fences. Range: ≥ 1, ≤ 5
`picket_width`	number	mm or in	no	Width of one picket/board in millimetres (metric) or inches (imperial). Optional; enables the picket count. Range: > 0, ≤ 1000
`picket_gap`	number	mm or in	default 0	Gap between pickets (0 for a solid privacy fence), in mm or in. Range: ≥ 0, ≤ 1000

Outputs

Output	Type	Unit	Description
`fence_length_m`	number	m	total_length − gates × gate_width.
`fence_length_ft`	number	ft	Same length in feet.
`sections`	integer		ceil(fence_length / post_spacing).
`posts`	integer		sections + gates + 1 (straight run; gate posts included).
`actual_post_spacing_m`	number	m	fence_length / sections.
`actual_post_spacing_ft`	number	ft	Actual spacing in feet.
`rails`	integer		sections × rails_per_section.
`pickets`	integer		ceil(fence_length / (picket_width + picket_gap)); only when picket_width is given.

Example

100 ft, 8 ft spacing, one 4 ft gate, 2 rails, 5.5 in pickets with 0.5 in gap: {"unit_system":"imperial","total_length":100,"post_spacing":8,"gates":1,"gate_width":4,"rails_per_section":2,"picket_width":5.5,"picket_gap":0.5} → {"fence_length_ft":96,"fence_length_m":29.26,"sections":12,"posts":14,"actual_post_spacing_ft":8,"rails":24,"pickets":192}

30 m, 2.4 m spacing, no gate, 3 rails, 90 mm pickets with 10 mm gap: {"unit_system":"metric","total_length":30,"post_spacing":2.4,"gates":0,"rails_per_section":3,"picket_width":90,"picket_gap":10} → {"fence_length_m":30,"sections":13,"posts":14,"actual_post_spacing_m":2.308,"actual_post_spacing_ft":7.571,"rails":39,"pickets":300}

GET https://tttkmbb.com/api/v1/calculate/fence?unit_system=imperial&total_length=100&post_spacing=8&gates=1&gate_width=4&rails_per_section=2&picket_width=5.5&picket_gap=0.5

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/fence (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/fence · Markdown: https://tttkmbb.com/construction/fence.md · JSON definition: https://tttkmbb.com/construction/fence.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="fence"
OpenAPI operationId: estimate_fence_materials
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Lowe's – How to build a wood fence (posts 6–8 ft on centre, 3 rails for 6 ft pickets) (reference)

FAQ

How deep should posts go?

About one third of the post length, below the local frost line: a 1.8 m (6 ft) fence typically uses 2.4 m (8 ft) posts set 60 cm (2 ft) deep in concrete.

Why are the actual spacings smaller than the maximum?

The run is divided into equal sections so that no bay exceeds post_spacing; e.g. 30 m at a 2.4 m maximum needs 13 sections of 2.31 m.

Related calculators

Decking Calculator — Boards and joists for a deck alongside the fence.
Concrete Slab Calculator — Bags of concrete for post footings.
Cylinder Calculator — Volume of a round post hole.