A complete material takeoff for a straight fence run: posts from the length and spacing, rails, boards from board width and gap, and the post-hole concrete volume for your planned hole size — metric first.
What Your Results Mean
Measure the run from end post to end post along the ground, in straight sections. A fence that turns a corner is two runs — measure each separately and add the takeoffs, and put a post at every corner and gate. Sloping ground complicates the board count (boards step or rake to follow the grade), so treat the result on a slope as a base figure and allow extra.
Post spacing sets the strength of the whole fence. 2.4 m (8 ft) between posts is the common maximum for closeboard and panel-style fencing; 1.8–2.4 m suits exposed sites, tall fences and heavier cladding. When the run doesn't divide evenly by your spacing, redistribute: a 20 m run at a nominal 2.4 m is 9 equal bays of 2.22 m, which looks far better than eight bays plus a 0.8 m stub at the end.
Rails run horizontally between posts, usually two per bay for fences up to about 1.2 m (4 ft) and three for taller fences so boards are held near top, middle and bottom — practice varies by region and style. The rail length in the results is the total metres of rail stock; buy lengths that match your bay spacing where possible, and expect offcuts. The board count comes from the board-plus-gap pitch: 150 mm boards with a 10 mm gap repeat every 160 mm, so a 20 m run needs 20 ÷ 0.16 = 125 boards. For vertical board fences you buy by count and cut each board to height; the board-run row is the linear metres of fence face, which is what matters for horizontal cladding and cap rails.
Post holes want a diameter around three times the post's thickness — 25 cm (10 in) is typical for a 10 cm (4 in) post — and a depth that buries roughly a third to half of the post's total length, or reaches below the local frost line where the ground freezes. Requirements vary by climate, so check what local fencers do; 60 cm (24 in) suits a typical 1.8 m fence in many temperate areas. Concrete is the standard setting for gates, corners and exposed runs; tamped gravel backfill is a well-established alternative that drains freely and is easier to adjust or replace, and it suits wet soils where a concrete collar can trap water against the post. Whichever you use, brace every post plumb while the setting cures — loading a fresh post with rails is how fences start life leaning.
What the Results Mean
- Posts: every post in the run including both ends — add extra for corners and gate uprights.
- Rail Length: total metres of rail stock at your rails-per-bay count, before offcut losses.
- Boards: vertical boards or pickets to clad the run at your width and gap.
- Board Run: the linear metres of fence face — equals the run length.
- Post-Hole Concrete: volume for neat cylindrical holes at your diameter and depth. Oversized or crumbling holes take more.
The Math Behind the Calculator
The fence is built from bays: the run divided by the post spacing, rounded up, with one more post than bays. Everything else keys off that count.
bays = ceil(run ÷ spacing)
posts = bays + 1
rails_m = bays × rails_per_bay × spacing
boards = ceil(run ÷ ((board_width + gap) ÷ 1000))
concrete_m³ = posts × π × (hole_∅_cm ÷ 200)² × (depth_cm ÷ 100)
The concrete formula is the cylinder volume πr²h per hole, with the hole diameter halved to get the radius in metres. A 25 cm hole is a 0.125 m radius, so a 60 cm deep hole holds π × 0.125² × 0.6 ≈ 0.0295 m³ — about 29.5 litres. The rail length uses nominal spacing; if you redistribute posts evenly (as on the 20 m example below), the true figure shortens slightly, so treat the calculated figure as the buy-with-margin number.
Worked Example: 20 m Run at 2.4 m Spacing
A straight 20 m run with posts at 2.4 m, two rails per bay, 150 mm boards with 10 mm gaps, and 25 × 60 cm post holes.
- Bays: 20 ÷ 2.4 = 8.33 → 9 bays, redistributed evenly at 20 ÷ 9 ≈ 2.22 m each.
- Posts: 9 + 1 = 10 posts.
- Rails: 9 × 2 × 2.4 = 43.2 m of rail at nominal spacing (40 m if set at the redistributed 2.22 m — buy to the nominal figure and let offcuts cover mistakes).
- Boards: pitch = (150 + 10) ÷ 1000 = 0.16 m; 20 ÷ 0.16 = 125 boards.
- Concrete per hole: π × 0.125² × 0.6 ≈ 0.0295 m³; for 10 posts: 10 × 0.0295 ≈ 0.29 m³ (about 295 L — roughly 26 × 25 kg bags of pre-mixed concrete at a typical 11.7 L yield per bag).
Check the concrete arithmetic in bag terms if you like: 295 L ÷ 11.7 L per bag = 25.2 bags, so 26 on the shelf. If gravel backfill replaces concrete on part of the run, subtract those holes — each one saves about 29.5 L of mix and asks for roughly the same volume of compacted gravel instead.
Reminder
These are planning quantities. Post depth and hole size vary by climate, soil and fence height, and boundary fences are regulated in many places — check local rules on heights, boundaries and materials before you dig. Call utility location services before any excavation.
Assumptions & Limitations
Every number above rests on these constants. If your fence differs, change the matching input — or read the linked guide for the full reasoning.
- Straight, level run; corners, gates and slope changes need extra posts and boards
- 25 × 60 cm holes are typical, not universal — bury a third to half the post length or go below frost line as your climate requires
- Concrete volume assumes neat cylindrical holes; loose or oversized holes take more
- Rail length uses nominal spacing — allow 5–10% for offcuts and splice waste
- Board count assumes full-height vertical boards with an even gap; patterned tops add spare boards