Fence calculator: steel fence kits and concrete

How this example system works

This calculator uses the CMI Western Australia guide: 2.37 m nominal panel width, with each panel kit containing two post pieces, two rails, three infill sheets and 15 screws. The guide also lists seven screws per fence-post assembly. The output separates panel-kit post pieces from standard post positions so you can compare the estimate with the supplier’s kit list.

For each straight run, the calculator rounds up to whole panel widths and adds one standard support position per run end. Corners and slope transitions add positions, each gate adds two separate gate posts. Measure fence-only runs without the gate opening. Concrete quantities use CMI’s soil-specific allowance for standard fence-post holes only. The guide calls for gate holes 10 mm deeper, so the calculator leaves gate-post concrete out rather than assuming the standard allowance applies.

The guide specifies a minimum 200 mm hole diameter and gives rocky, clay/firm and sand/loose soil examples at 300, 600 and 900 mm depths. Actual soil, wind, marine exposure, local council requirements and the chosen fence design may require different foundations. This is one supplier’s WA system example, not a national Australian standard.

Formula

• Count panel kits and run posts

  Panel kits = ceil(fence-only length ÷ 2.37 m) Run posts = panel kits + 1 per straight run + extra corner or slope positions

  The 2.37 m width comes from the cited CMI Western Australia kit guide.

• Add gate posts and post mix

  Gate posts = 2 × number of gates Post-mix bags = sum of the sourced soil allowance for each standard post hole

  Gate-post concrete is not included because the guide does not give a separate gate-hole quantity.

Worked example

1. 1

   Round up the panel kits

   ceil(10.00 m ÷ 2.37 m) = 5 kits

   The example has one 10 m fence-only run and one separate gate.

2. 2

   Count posts and kit pieces

   5 kits + 1 = 6 standard post positions 5 kits × 2 post pieces = 10 kit post pieces

   The final bay may need adjustment to fit the available space.

3. 3

   Count intermediate assemblies and screws

   5 kits − 1 single-run end allowance = 4 intermediate assemblies 4 × 7 assembly screws = 28 screws

   The two single end posts do not use the intermediate assembly allowance.

4. 4

   Estimate rocky-soil post mix

   6 standard holes × 1 × 20 kg = 6 bags

   This uses the CMI guide’s rocky-soil allowance for the example hole. Gate-post concrete is excluded.

Check before installation

Use the selected kit’s current installation guide, confirm local council requirements, and ask the supplier about wind or marine conditions. The CMI guide describes stepped or raked installation, the calculator treats each entered slope step as one additional support position. It does not design footings, check structural loads or determine a compliant fence.

Frequently asked questions