Standard fence-framing conventions
| Item | Typical convention |
|---|---|
| Post spacing | ≈2.4 m common default for lightweight picket fencing; heavier fences or higher wind exposure often use closer spacing |
| Concrete per post hole | ≈2 × 20 kg pre-mixed bags — varies with post size, hole depth and soil conditions |
| Rails per section | 2 typical for standard-height picket fences; taller fences commonly use 3 or more |
- Post-hole depth and concrete quantity depend on post size, fence height, local wind exposure and soil conditions — and, critically, on the local frost depth in cold climates, where posts generally need to be set below the frost line to prevent heaving. Check local building code or a fencing contractor for the required depth in your area.
- This calculator estimates material counts for a straight run of fence; gates, corners, and changes in direction typically need additional posts and hardware beyond this basic estimate.
What does a fence calculator do?
A fence calculator estimates the number of posts, rails, pickets and post-hole concrete bags needed to build a picket-style fence of a given length, based on the post spacing (section length), the number of horizontal rails per section, and the picket width and gap. It follows standard residential fence-framing conventions: one post at each spacing interval plus one extra to close the run, and one concrete bag allowance per post hole.
Post spacing (the distance between posts, defining one 'section' of fence) is commonly chosen based on rail length availability, wind loading and the fence style, with roughly 2.4 m being a common default for lightweight picket fencing. Pickets are estimated by dividing the total fence length by the width of one picket plus its gap, since pickets and gaps repeat continuously along the fence length regardless of section boundaries.
How to use this fence calculator
- Enter the total fence length, in meters.
- Enter the post spacing (the length of one fence section between posts), in meters.
- Enter the number of horizontal rails per section (commonly 2 for a standard picket fence, more for taller fences).
- Enter the picket width and the gap between pickets, in millimeters, and read the estimated posts, rails, pickets, sections and concrete bags.
The formula behind fence material quantity
The number of sections equals the fence length divided by the post spacing, rounded up. Posts equal sections + 1 (each section shares a post with its neighbor, plus one extra post to close the run). Rails equal sections × rails per section. Pickets equal the fence length divided by (picket width + picket gap), rounded up. Concrete bags are estimated at 2 bags of 20 kg pre-mixed concrete per post hole, a commonly used residential fence-post setting convention.
Worked example: a 30 m fence at 2.4 m post spacing with 2 rails per section, 90 mm pickets and a 5 mm gap needs sections = ⌈30 ÷ 2.4⌉ = 13, posts = 14, rails = 13 × 2 = 26, and pickets = ⌈30 ÷ 0.095⌉ = 316. Concrete is estimated at 14 posts × 2 bags = 28 bags of 20 kg pre-mixed concrete.
Common mistakes
- Setting fence posts above the local frost line in a cold climate, which can cause posts to heave and shift over winter freeze-thaw cycles.
- Forgetting to add extra posts for gates and corners, which this straight-run estimate does not include.
- Underestimating concrete needed for larger posts or deeper holes than the standard 2-bag convention assumes.
- Miscalculating picket count by forgetting to include the picket gap in the repeat-width calculation.
Perguntas frequentes
How many fence posts do I need for 30 m?
At a common 2.4 m post spacing, a 30 m fence needs ⌈30 ÷ 2.4⌉ = 13 sections and therefore 14 posts (sections + 1), before accounting for any gates or corners.
How much concrete per fence post?
A commonly used residential estimating convention is about 2 bags of 20 kg pre-mixed concrete per post hole, though the actual amount depends on post size, hole depth and diameter, and soil conditions.
How deep should fence posts be set?
Post depth depends on fence height, post size and local conditions — in cold climates, posts generally need to be set below the local frost line to prevent frost heave, a requirement set by local building code rather than a fixed universal depth.
How many pickets do I need for a fence?
Divide the total fence length by the width of one picket plus its gap. A 30 m fence with 90 mm pickets and a 5 mm gap needs about 316 pickets, since pickets and gaps repeat continuously along the fence length.
Does this calculator account for gates and corners?
No — it estimates material for a straight run of fence only. Gates, corners and changes in direction typically require additional posts, hardware and hinges beyond this basic straight-run estimate.
Referências
- Standard residential fence-framing conventions for post spacing, rail count and post-hole concrete allowance, as commonly described in fencing and hardscaping trade guides.
- International Code Council (ICC) — International Residential Code (IRC) and local building codes set frost-depth and post-setting requirements that vary by climate zone.
- Manufacturer/supplier concrete bag yield data — the 20 kg pre-mixed bag convention used here should be checked against the specific product being purchased.