For most residential gates, a 75x75 mm galvanised steel SHS or a 100x100 mm timber post typically handles pedestrian and single driveway gates, set into a depth of concrete footing generally recommended for standard gates. Wider or heavier driveway gates and double leaf setups need 100x100 to 125x125 mm SHS with 600–900 mm embedment, depending on height and wind exposure. Soil type, bracing, and automation all shift these numbers, so treat them as a starting point rather than a final spec.
TL;DR:
- Pedestrian gates up to 1.1 meters wide typically require 75x75 mm steel or 100x100 mm timber posts set in 450–600 mm deep footings.
- Larger or automated driveway gates demand 100x100 to 125x125 mm steel sections with at least 600 mm embedment, increasing to 750–900 mm for heavier, wider, or taller gates.
- Post wall thickness must be at least 2.5 mm for standard posts, with 4 mm recommended for larger, heavier, or automated gates to prevent flexing and ensure durability.
- Proper installation involves setting posts plumb before concrete cures, using braces, and ensuring adequate drainage, especially in poor soil or high-wind conditions.
- For complex or heavy gate projects, hiring a professional ensures correct sizing, engineering, and installation, particularly when automation or difficult site conditions are involved.
Table of Contents
- Recommended gate post sizes by gate type
- How deep does a gate post footing need to be?
- Timber, steel, or aluminium: which post material actually holds up?
- How do you size a post from your gate's width and weight?
- Getting the installation right on-site
- What fabricators change once they see the site
- When is it worth hiring a professional instead of DIYing?
- Need a gate built to the right spec the first time?
- Sources
- FAQ
Recommended gate post sizes by gate type
The right post section depends almost entirely on what the gate is doing, not just how it looks. A pedestrian gate swinging on light hinges asks very little of its posts compared to a driveway gate copping wind load and the torque of a motor.
Pedestrian gates (up to 1.1 m wide) are the easiest case. A 75x75x2.5 mm SHS steel post or a 100x100 mm timber post is generally sufficient, and CAD60's design tables show a common pairing of 1000 x 1800 mm gates with exactly this 75x75x2.5 SHS post size. These gates carry light loads and rarely see much wind resistance because of their narrow frame.
Garden and small vehicle gates need a step up. Once you're swinging something wider than a standard pedestrian gate, or the leaf carries decorative ironwork, move to a 75–100 mm steel section or stick with 100x100 timber. The extra bulk matters more for resisting twist over years of use than for handling the static weight.
Driveway gates, single and double leaf, are where post size decisions actually matter. A single leaf driveway gate typically wants 100x100 SHS, while double leaf gates spanning wide openings, or any leaf carrying an automation motor, often justify stepping up to 125x125 SHS. Fabrication guidance for swing and bi-fold gates backs this up: lighter swing gates up to a metre can get away with 50 mm square aluminium if properly braced, but heavier gates spanning up to four metres commonly need 75–125 mm square galvanised steel with adequate wall thickness.
Wall thickness matters as much as the outer dimension. A 75x75 SHS with 2.5 mm walls flexes noticeably more than the same section at 3 mm or 4 mm, and that difference shows up first at the hinge welds.
Typical starting points by gate category:
- Pedestrian gate (≤1.1 m): 75x75 mm SHS steel or 100x100 mm timber
- Garden or narrow vehicle gate: 75–100 mm steel section or 100x100 timber
- Single driveway leaf: 100x100 mm SHS, 2.5–3 mm wall
- Double leaf driveway gate: 100x100 to 125x125 mm SHS per post
- Heavy, wide, or automated leaves: 125x125 mm SHS with 4 mm wall minimum
Bracing affects the sizing requirements. A braced gate post, tied back to a fence line or supported by a diagonal strut, can perform adequately at a smaller size than an unbraced, freestanding post carrying the same gate. If your post is isolated with nothing on either side, it is better to choose a larger post rather than relying solely on the concrete footing.
How deep does a gate post footing need to be?
Embedment depth is where most DIY gate installs go wrong, usually by going too shallow. Finlayson's residential timber fencing datasheet recommends around 450 mm of embedment for fences up to 1,200 mm high, stepping up to 600 mm for fences between 1,200 and 1,800 mm, with hole diameters of at least 300 mm.
Statistic to remember: that 600 mm figure isn't arbitrary padding, it's the depth Wyndham City's technical specification settles on for many standard gate post installations, and it lines up with CAD60's fabrication examples, where a 100x100 SHS post supporting a 1000 x 2000 mm gate sits in a 300 mm diameter footing at 600 mm depth. Taller or heavier gates step up to 750–900 mm depth in 400 mm diameter footings.
Installing a footing correctly follows a fairly fixed sequence:
- Dig to the required depth and diameter, adding roughly 50–75 mm of compacted gravel at the base for drainage.
- Position the post plumb, check it against a level on two faces, and confirm hinge height and swing clearance before anything sets.
- Brace the post temporarily with timber props on two sides so it can't shift while curing.
- Pour concrete in layers, tamping to remove air pockets, and finish with a slight slope away from the post to shed water.
- Leave it to cure for at least 48 hours before hanging the gate, longer in cold weather.
Poor soils change all of this. Sandy or reactive clay soil, high wind exposure, or gates over roughly 1.8 m tall are the point where a rule-of-thumb footing stops being reliable. That's when it's worth getting an engineer to size the footing properly rather than guessing at a bigger hole and hoping.
Timber, steel, or aluminium: which post material actually holds up?
Each material solves a different problem, and picking the wrong one shows up as a maintenance headache within a few years, not immediately.
Timber posts, usually 100x100 mm hardwood, are cheap, easy to work with hand tools, and forgiving of small imperfections in a DIY build. Their weakness is moisture. A post buried without drainage or a capped top will rot from the inside well before the visible timber looks tired, so gravel at the footing base and a bevelled or capped top that sheds water aren't optional extras, they're what determines whether the post lasts ten years or thirty.
Galvanised steel is the standard for anything carrying real load or motorised automation. Subdivision specifications commonly list 60 mm outside diameter pipe for gate, corner, and strainer posts, against 42 mm for intermediate posts, and council technical specs generally mandate tubular steel frames built to AS 4680 with galvanised fittings throughout. Stick with standard galvanising for most residential work; step up to a thicker wall or stainless fittings only in coastal or heavy industrial settings where corrosion runs faster than normal.
Aluminium earns its place on light, unmotorised gates where weight matters more than strength, think a narrow garden gate you want easy to swing by hand. It's a poor choice for anything wide, heavy, or automated, because it flexes under torque in a way steel simply doesn't.
Pro Tip: Match your post material to your hinge hardware, not just your fence. A galvanised post with cheap zinc-plated hinges will rust at the fixing points years before the post itself fails.
- Timber: cheapest, easiest to cut, needs drainage and capping to last
- Galvanised steel: best for load and automation, standard for driveway gates
- Aluminium: fine for light garden gates, unsuitable for heavy or motorised leaves
How do you size a post from your gate's width and weight?
Measuring your actual gate, rather than guessing from a photo online, is the fastest way to avoid an undersized post. Start with two numbers: the width of the opening and a rough weight estimate for the leaf.
The mapping that fabricators use most often looks like this:
- Pedestrian gate, ≤1.1 m wide: 75x75 mm SHS or 100x100 mm timber
- Residential gate, 1.0–1.8 m wide: 75–100 mm SHS or 100x100 timber
- Wide or heavy single leaf, 1.8–3 m: 100x100 mm SHS minimum
- Double leaf openings over 3 m, or any motorised leaf: 100–125 mm SHS
Height changes the footing more than the post section. Finlayson's timber datasheet puts an 1,800 mm gate at roughly 600 mm embedment, while a 2,100 mm gate typically wants 750–900 mm depth to keep the leverage at the top of the gate from working the post loose over time.
Three worked examples make the pattern concrete:
A 1 m pedestrian gate, standard height, needs nothing more than 75x75 SHS posts at 450–600 mm embedment in a 300 mm diameter footing. It's a straightforward weekend job for most DIYers.
A 3 m driveway leaf, single swing, sits at the point where 100x100 SHS becomes the sensible minimum, paired with 600 mm embedment. If that leaf carries decorative wrought iron work rather than plain steel infill, the added weight pushes you toward 125x125 posts even at this width, particularly if it's ever likely to be automated later.
A 5 m double leaf driveway gate is genuinely heavy engineering by DIY standards. Each leaf runs 2.5 m, the combined swing load is substantial, and 125x125 mm SHS with 750–900 mm embedment in 400 mm diameter footings is a realistic starting point, not an overspec. Anything at this scale, especially with automation in the plan, is worth running past an engineer or an experienced fabricator before you commit to a footing size.
Getting the installation right on-site
A correctly sized post still fails if it's installed poorly, and most gate problems trace back to installation shortcuts rather than the post spec itself.
Fit the gate to its posts before the concrete goes in, not after. Stratco's installation guide recommends this sequence specifically, along with offsetting gate posts around 25 mm from adjacent fence posts to give the swing proper clearance.
- Set both posts plumb and square first, checking diagonal measurements match before you brace anything.
- Hang the gate temporarily to confirm hinge height, swing clearance, and closing gap, adjusting post position while the concrete is still workable.
- Fix hinges with anti-lift collars on driveway gates, since a gate without them can be lifted off its hinges, a common security gap.
- Weld or bolt gussets at hinge mounting points on steel posts to spread the local stress that concentrates there over years of swinging.
- Slope the top of timber posts and avoid soil mounding around the base, both of which trap moisture against the post.
Hinge count follows gate height: two hinges suit most gates under 1,200 mm, while Finlayson's guidance calls for three hinges on gates over 1,200 mm to spread the load across the frame properly.
Pro Tip: A small gravel drain routed at the base of the footing, even just a shovel-width trench filled with gravel, stops water pooling against the post and adds years to timber life in particular.
The most common failure isn't the post size at all, it's a shallow footing, weak temporary bracing that lets the post drift before curing, or forgetting to account for the closing gap and finding the gate binds against the latch post six months later.
What fabricators change once they see the site
Installers who quote gate jobs for a living rarely size posts off a table alone. Automated gates get the biggest jump: motor torque and the repeated cycling of an opener put more strain on a post than a hand-swung gate ever will, so fabricators commonly increase wall thickness or step up a full section size specifically to give the motor mount something solid to bolt into.
Before quoting, most fabricators ask for photos of the existing opening, ground conditions, and any nearby structures, plus exact width and height measurements rather than estimates. On-site, small fixes make an outsized difference over time: gussets welded at hinge points, anti-lift collars on driveway gates, and a proper base plate where a post mounts to an existing slab rather than into soil.
When is it worth hiring a professional instead of DIYing?
Automated gates, heavy wrought iron leaves, or a site with poor soil or unusual wind exposure are where I'd stop reaching for a rule-of-thumb table and call a fabricator. A professional brings engineered footing calculations, welded fabrication rather than bolted joints, and proper automation wiring with a workmanship warranty behind it, things that are genuinely hard to replicate with a post-hole digger and a bag of concrete.
If you're determined to DIY, photograph the full opening, measure width and height precisely, and note your soil type before you start. That homework alone prevents most of the expensive mistakes.
Need a gate built to the right spec the first time?
Getting post sizing right on paper is one thing. Getting it right on a site with tricky soil, an automation motor to mount, or a heavy custom leaf is where most DIY plans hit their limit. A local gate fabricator with extensive experience may design and fabricate custom gates using locally sourced materials, engineering the post, footing, and gate as a unified system rather than relying solely on generic rules of thumb.
That matters most for the jobs this article flags as genuinely tricky: wide double leaf driveway gates, decorative wrought iron gates with real weight to carry, and anything getting an automation motor down the track. For straightforward residential gates, Vicgates handles the full process end to end, from design rendering through to installation, so you're not left guessing whether a 100x100 or a 125x125 post is the right call. Commercial and industrial projects needing heavier-duty gates, fencing, and automation get the same tailored approach.
If your project fits any of those categories, request a design consult and get a spec built around your actual site, not a generic table.
Sources
- Finlayson — Residential timber fences technical datasheet
- Wyndham City technical specification — Section 707 fencing and gates
- City of Swan subdivision specification — galvanised posts and gates
- CAD60 — Standard pedestrian gate sizes in Australia
FAQ
What size should a gate post be?
For most pedestrian and single driveway gates, 75x75 mm to 100x100 mm SHS steel or 100x100 mm timber handles the job. Wider driveway leaves, double gates, or automated gates typically need 100x100 to 125x125 mm SHS, with the exact call depending on gate weight, height, and wind exposure.
Will a 4x4 post hold a gate?
A 100x100 mm (commonly called "4x4") timber post holds most pedestrian and light garden gates fine, provided it's embedded to at least 450 mm and capped to shed water. It's undersized for wide driveway leaves or anything carrying an automation motor, where a heavier steel section performs more reliably over time.
What size steel post should I use for a gate?
75x75 mm SHS suits pedestrian gates up to 1.1 m wide, while single driveway leaves generally want 100x100 mm SHS. Double leaf or automated driveway gates often step up to 125x125 mm SHS, and fabrication guidance recommends checking wall thickness alongside the outer dimension, not just the section size.
What size post is needed for a driveway gate?
Single driveway gates typically use 100x100 mm SHS steel posts set 600 mm deep in a 300 mm diameter concrete footing. Double leaf or heavier driveway gates commonly need 125x125 mm SHS with 750–900 mm embedment, particularly once automation is added to the mix.
How deep should a gate post footing be?
Timber technical guidance recommends around 450 mm embedment for gates up to 1,200 mm high and 600 mm for gates between 1,200 and 1,800 mm. Taller gates, over roughly 1,800 mm, generally need 750–900 mm depth to keep the post stable under load.