How far apart should fence posts be?

For a timber paling fence, Timber Queensland's data sheet sets a maximum of 2400 mm with 100 x 38 hardwood or 90 x 35 treated pine rails, and 2100 mm with 75 x 38 hardwood or 70 x 45 treated pine rails. Colorbond style fences are set by the panel: BlueScope's guide gives post centres of the bottom rail length plus 10 mm, typically 2350 to 2365 mm.

How deep do fence posts go?

Timber posts go about 450 mm into the ground for fences up to 1200 mm high and 600 mm for fences up to 1800 mm (Timber Queensland). For Colorbond style fences, BlueScope's guide sets the footing by soil: 400 mm in rock, 600 mm in clay or firm earth and 900 mm in sand or loose fill, for wind regions A and B.

How many palings per metre?

Divide 1000 mm by the paling width plus any gap. Butted 100 mm palings are 10 per metre. A lapped fence with 150 mm base palings at 50 mm gaps and 100 mm palings over the gaps also comes to 10 per metre, in two layers.

How much concrete per fence post?

Work out the hole volume, subtract the post, and use about 110 twenty kilogram bags per cubic metre. A 300 mm hole 600 mm deep with a 90 x 70 post is about 4 bags. BlueScope's Colorbond guide gives 1, 2 or 3 bags per 200 mm hole for rock, clay or sand.

Does it count gates, corner and end posts?

Gate openings come off the fence length and add a post each, and joined runs share their corner posts. Gates themselves, and the heavier end, corner and gate posts, aren't counted because they vary by supplier.

Free calculator

Fence calculator

For a 1.8 m timber paling fence, set posts no more than 2.4 m apart with 100 x 38 hardwood or 90 x 35 treated pine rails, 600 mm into the ground, with three rails. Posts = bays + 1 per run. A Colorbond style fence usually has posts at 2350 to 2365 mm centres, one panel per bay.

Your job

Fence type

Runs

Run 1 length

Gates

Gate opening

Gate openings come off the fence length and add a post each. Gates themselves aren't counted.

Height and spacing

Fence height

Up to 1800 mm (what the Timber Queensland guide covers). Posts go 450 mm deep up to 1200 mm high, 600 mm above that.

Rail size

Post spacing

Maximum 2.4 m with these rails.

Palings and plinths

Paling width

Plinths (one per bay)Concrete footings (untick for rammed earth)

Detail drawn to scale: posts, rails, infill and the footings below ground.

Posts

2,400 mm long, 600 mm in the ground

Rails

3 rows, 4.8 m lengths (2 bays each)

Palings

200

100 mm butted

Plinths

One per bay

Concrete

43× 20 kg

300 mm holes

The working, with your numbers

1. Fence length20.00 m= 20.00 m
2. Bayseach run ÷ 2.40 m, rounded up= 9
3. Postsbays + 1 per run= 10
4. Rails3 rows × (bays ÷ 2, rounded up, per run)= 15
5. Palings20,000 mm ÷ 100 mm= 200
6. Concrete(π × 0.15² − 0.09 × 0.07) × 0.6 × 10 × 110= 43 × 20 kg

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The formula, in plain words

1Fence length = the total of every run, minus the gate openings.
2Bays per run = run length divided by post spacing, rounded up. Posts = bays + 1 per run; runs that meet at a corner share that post, and each gate adds one post.
3Timber paling (Timber Queensland data sheet 20): posts go 450 mm deep for fences up to 1200 mm high and 600 mm deep up to 1800 mm. Two rails up to 1200 mm high, three above that. Each rail spans two bays, so rails per row = bays ÷ 2, rounded up.
4Palings = fence length ÷ (paling width + gap), rounded up. Lapped palings (150 mm base at 50 mm gaps with 100 mm over-palings) come to 10 per metre. One plinth per bay.
5Concrete per post = (hole area − post area) × depth, with a 300 mm hole. Bags = total volume × 110 twenty kilogram bags per m³, rounded up.
6Colorbond style: panels = bays at your post centres. Each panel has a top and bottom rail and 3 infill sheets (4 on 3100 mm panels). Footings are 200 mm holes: rock 400 mm deep and 1 bag, clay 600 mm and 2 bags, sand 900 mm and 3 bags. Post length = (footing depth − 40) + height + 50, rounded up to a 2100, 2400, 2700 or 3000 mm post.

Worked example

A 20 m timber paling fence, 1800 mm high, posts at 2.4 m with 90 x 35 treated pine rails, 100 mm palings butted, plinths, and 90 x 70 posts concreted in 300 mm holes.

1.Bays: 20 ÷ 2.4 = 8.33, rounded up to 9. Posts: 9 + 1 = 10, each 1800 + 600 = 2400 mm long.
2.Rails: 3 rows × (9 ÷ 2 = 4.5, rounded up to 5) = 15 rails, each 4.8 m (two bays).
3.Palings: 20,000 mm ÷ 100 mm = 200 palings. Plinths: one per bay = 9.
4.Concrete per post: (π × 0.15² − 0.09 × 0.07) × 0.6 = 0.0386 m³. Ten posts = 0.386 m³ × 110 = 42.5, rounded up to 43 bags.

Answer: 10 posts at 2400 mm, 15 rails at 4.8 m, 200 palings, 9 plinths and 43 × 20 kg bags of concrete.

How to measure it

Measure each straight run of fence along the boundary. Add a run for every change of direction.
Tick 'Runs meet at corners' if the runs join up, so the corner posts are only counted once.
Count the gates and their openings. The openings come off the fence length.
For Colorbond style fencing, check your supplier's post centres: they vary by brand.

Where the numbers come from

Every default in the calculator is a number a supplier or manufacturer publishes. We list the source next to it so you can check.

What	Value	Source
Max post spacing with 100x38 hardwood or 90x35 treated pine rails	2,400 mm	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Max post spacing with 75x38 hardwood or 70x45 treated pine rails	2,100 mm	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Post depth in the ground, fences 1200 to 1800 mm high	600 mm	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Rails per bay, fences up to 1200 mm high (3 above that)	2 rails	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Minimum post hole diameter	300 mm	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Lapped: 150 mm base palings at 50 mm gaps plus 100 mm over-palings	10 palings per m	Hume City Council fencing specification (2015) (checked 2026-09-30)
Treated pine plinth, one per bay (125 x 38 hardwood)	120 x 35 mm	Timber Queensland Technical Data Sheet 20, Residential Timber Fences (2014) (checked 2026-09-30)
Premixed concrete, 20 kg bags needed for one cubic metre	110 20 kg bags per m³	Cement Australia slab calculator (checked 2026-09-21)
Post centres: bottom rail length + 10 mm, typically 2350 to 2365 mm	2,365 mm	BlueScope, COLORBOND steel fencing installation guide (2016) (checked 2026-09-30)
Footing hole diameter	200 mm	BlueScope, COLORBOND steel fencing installation guide (2016) (checked 2026-09-30)
Footing by soil: rock 400 / 1 bag, clay 600 / 2, sand 900 / 3 (wind regions A and B)	600 mm deep, 2 bags	BlueScope, COLORBOND steel fencing installation guide (2016) (checked 2026-09-30)
Infill sheets per standard panel (4 on 3100 mm panels)	3 sheets	Lysaght Fencing Design and Installation Guide, Non-Cyclonic (2026) (checked 2026-09-30)
Post length = (footing depth - 40) + height + 50, rounded up to 2100/2400/2700/3000	50 mm clearance	Lysaght Fencing Design and Installation Guide, Non-Cyclonic (2026) (checked 2026-09-30)

Manufacturers named here are the source of the number, not a recommendation. Confirm quantities with your supplier.

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