A fence is really two builds: the panels everyone sees, and the footings nobody does. Panels are the easy 80%: our step-by-step installation guide covers that: but the buried 20% decides whether it is still straight in ten years.
The quick answer
Rule of thumb: bury about one third of the post’s above-ground height: roughly 600 mm for a 1.8 m fence.
Dig holes about three times the post width: around 200 to 300 mm across.
Allow two to four 20 kg bags of rapid-set concrete per hole.
Cure overnight (rapid-set) or longer (mixed) before hanging panels.
Lodge a free Before You Dig Australia (BYDA) enquiry first.
Why footings are the make-or-break 20% of a DIY fence
An aluminium fence is light but broad, so it works like a sail: every gust is levered against the concrete below ground. A shallow footing does not snap: it slowly tilts, taking the whole run with it. And footings are the one part you cannot fix later without digging out set concrete.
How deep should fence posts be?
The common Australian rule of thumb is to bury about one third of the post’s height above ground: roughly 600 mm deep for a standard 1.8 m fence. Treat these as guidance, not engineering; soil, wind and height all shift the answer.
| Fence height | Typical footing depth | Typical hole diameter |
|---|---|---|
| 1.2 m | 400 to 450 mm | 200 to 250 mm |
| 1.5 m | 500 to 550 mm | 200 to 300 mm |
| 1.8 m | Around 600 mm | 250 to 300 mm |
| Over 1.8 m | 700 mm+: get advice | 300 mm+ |
Common DIY guidance only: not site-specific engineering or council requirements.
For diameter, aim for about three times the post width: most aluminium posts are 50 mm square, so a 200 to 300 mm hole gives a solid collar of concrete and room to nudge the post into line. Much of Brisbane, Logan and Ipswich sits on reactive clay that moves with moisture; coastal pockets are sandy. In either extreme, err deeper and wider.
Digging the holes: but call BYDA first
Before a spade goes in, lodge a free enquiry with Before You Dig Australia (BYDA: formerly Dial Before You Dig). It takes minutes online, plans arrive within days, and power, water, gas and NBN lines often sit shallower than a fence footing.
A post-hole shovel and digging bar handle a few holes; for a full run, hire a one-person petrol auger. In clay, dig a day or two after rain, and drop 50 to 100 mm of gravel in each hole for drainage.
Concrete: rapid-set or mixed, and how many bags?
Rapid-set post mix is the DIY favourite: it holds a braced post firm within the hour, with no barrow to clean. Standard concrete mix is cheaper per hole and worth considering on a long run or for gate posts.
As a realistic estimate, a 200 mm hole at 600 mm deep takes about two 20 kg bags; a 300 mm hole, closer to four. Count your holes and add a couple of spares.
Wet or dry pour? Most rapid-set products are poured dry around the braced post, then watered as directed; a wet mix blended in a barrow is slower but more consistent. Either way, follow the bag, not folklore.
Setting posts plumb, braced and evenly spaced
Run a string line between the ends of the run at a consistent height: every post face and top references it. Spacing is fixed by panel width: measure centre to centre and keep it identical at every bay; our guide to measuring for aluminium fencing shows how to plan post centres before you order.
Stand each post, check plumb on two adjacent faces with a spirit level, brace it, then pour. Re-check afterwards (posts drift the moment you look away) and dome the concrete so rainwater sheds away from the post.
How long before you can hang the panels?
Rapid-set is firm within the hour, but firm is not strong: keep braces on and give it a few hours (ideally overnight) before bolting panels on. Standard mixed concrete needs 24 to 48 hours before real load, and about a week for most of its strength. Set posts one day, hang panels the next, following the panel installation steps.
Slopes, slabs and other curveballs
On a sloping block you must choose between following the ground and stepping the panels: the choice changes your post heights, so read our raked vs stepped fencing guide before you dig. If your fence line follows an existing slab, you may not need holes at all: see our guide to fence posts on concrete for bolt-down base plates.
When to get professional advice
Rules of thumb cover a typical suburban boundary fence: and stop there. Get site-specific advice if your fence is taller than 1.8 m, on a wind-exposed site, or runs on or near a retaining wall: a wall built to hold soil was not necessarily built to hold a fence, as our guide to fencing on retaining walls in Queensland explains. Rather skip the digging? FY Fencing can arrange professional installation.
Frequently asked questions
How deep should fence posts be in Australia?
As a general guide, bury about one third of the post’s above-ground height: around 600 mm for a 1.8 m fence. Soft sand, reactive clay, tall fences and windy sites all call for deeper footings or professional advice.
How wide should a fence post hole be?
Aim for roughly three times the post width. Typical 50 mm aluminium posts suit a hole around 200 to 300 mm across: enough concrete on every side, with room to adjust the post before the mix sets.
How many bags of concrete do I need per fence post?
A 200 mm diameter hole dug 600 mm deep takes about two 20 kg bags of rapid-set post mix; a 300 mm hole takes closer to four. Multiply by your post count and keep a couple of spares handy.
How long should concrete cure before hanging fence panels?
Give rapid-set a few hours (ideally overnight) with braces left on; standard mixed concrete needs 24 to 48 hours before real load. Set posts one day, hang panels the next.
Do I need to contact Before You Dig Australia before fencing?
Yes. Lodge a free BYDA enquiry (formerly Dial Before You Dig) online before digging. Buried power, gas, water and communications lines can sit shallower than a fence footing; plans usually arrive within days.
Can I put fence posts on an existing concrete slab instead of digging?
Often, yes. If your fence line follows a sound slab, posts can be fixed with bolt-down base plates instead of dug-in footings. The concrete must be sound and thick enough to hold the anchors.
A note on these numbers. The depths, diameters and bag counts above are common DIY guidance for typical suburban aluminium fences: not engineering advice. Soil, wind, height and nearby structures all change what a footing needs; get site-specific advice if your block is unusual.
Working out what your fence line needs? Tell us the run and the height and we will quote it, supply-only or installed.
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