Size a gate motor to the heaviest real load it will see, not to the weight printed on the box. Start with the gate's actual weight, its length, how much wind it catches and how many times a day it runs. Then choose a motor rated well above that figure, because a motor that works near its limit overheats, wears out early and fails on the hottest or windiest day of the year.
This guide walks through each input, shows how sliding, single swing and double swing gates differ, and lists what to check once the motor is in. It is written for owners, builders and designers planning an automated entry in Victoria and elsewhere in Australia.
TL;DR
- Weigh or reliably estimate the gate first. Motor ratings are maximum figures, so leave a generous margin rather than matching the number.
- Length matters as much as weight. A long, light sliding gate or a long swing leaf can need a bigger motor than a short, heavy one.
- Wind, solid infill, a worn track or sagging hinges all raise the load. Fix the gate before you size the motor.
- Busy entries (shared driveways, commercial sites) need a motor chosen for duty cycle, not just weight.
- A professional installer should confirm the sizing, set the safety devices and test the gate after installation.
Table of Contents
- What you need to know before you size a motor
- Start with the gate, not the motor
- Sizing a sliding gate motor
- Sizing a swing gate motor
- Wind and the gate's face
- Duty cycle: how often the gate runs
- Power supply and cable runs
- A worked example
- Upgrading an old gate motor
- Perspective: why we over-specify the margin
- Safety and compliance in Australia
- Checks after installation
- Get the sizing right with us
- FAQ
- Sources
What you need to know before you size a motor
A supplier or installer can only size a motor properly with a handful of facts. Gather these first and the rest of the process is straightforward.
- Gate type. Sliding, single swing or double swing. The sizing logic differs for each.
- Weight. Per leaf for swing gates, the whole panel for sliding gates.
- Clear opening width and leaf length. For a sliding gate, that includes the tail that sits beyond the opening.
- Infill. Open pickets and slats shed wind. Solid sheet, privacy cladding or tight timber boards act like a sail.
- Condition. Track, rollers, hinges and posts. A gate that already binds will overload any motor.
- Usage. How many cycles a day, and whether they come in bursts, such as a school run or deliveries.
- Site. Slope, exposure to wind, distance to power, and whether the gate will run on mains or solar.
If you cannot weigh the gate, ask the fabricator for the material list and dimensions. Steel and timber gates vary a lot in mass, so a guess from appearance is unreliable. A heavy-looking aluminium gate can weigh far less than a plain-looking hardwood one.
Start with the gate, not the motor
The most common sizing mistake is shopping for a motor first. Buyers see a rating, such as "suits gates up to 500 kg", and assume any gate under that number is fine. That figure is a ceiling, not a target.
Before comparing any motor, make sure the gate itself moves freely. A sliding gate should roll with light hand pressure along the whole track. A swing gate should stay where you leave it at any point in its arc and not drift or drag. If it does not, the problem is mechanical and a bigger motor will only hide it for a while, then break something. We cover the checks that decide whether an existing gate can be automated in 4 gate checks that decide if you can automate your gate.
Sizing a sliding gate motor
Measure the opening and the tail
Measure the clear opening between the posts or pillars. A sliding gate also needs a tail, the section of gate that sits beyond the opening when it is closed, so the gate stays supported on its rollers. Many installers work to the opening plus roughly 400 mm for the counterbalance tail, though the right figure depends on the gate design. The total gate length is therefore longer than the opening, and that longer, heavier panel is what the motor has to move.
Also check the run-off space beside the opening. A gate that needs more room than the fence line allows may call for a different design, such as a telescopic or bi-fold arrangement. Our piece on sliding gate design, track, slope and safety covers the groundwork.
Weight, length and the margin
For sliding gates, weight is the headline figure, but length changes how hard the motor works. A longer gate travels further on every cycle, so the motor runs for longer, builds more heat and puts more strain on the rack and pinion.
A practical rule we use when talking to owners: choose a motor with a rated capacity comfortably above the gate's weight, not equal to it. A 400 kg gate suits a motor rated for more than 400 kg. A very long but light gate is a case for stepping up a size again, because of the extra running time.
A simple hand test gives a rough read on the load, though it never replaces weighing the gate. If one hand pushes the gate easily along the whole track, the gate is in good shape. If it takes real effort, the track, wheels or alignment need work before any motor goes on.
Slope and track
A slight fall across the driveway makes a gate drift one way and load the motor in the other. Level, clean, straight track keeps the load low and the motor cool. Where the ground slopes, the track and gate may need to be designed around it, not forced onto it.
Sizing a swing gate motor
Leaf length is the big lever
A swing gate behaves like a door: the longer the leaf, the more leverage the motor has to overcome, and the more wind it catches. A short, heavy leaf may be easier on a motor than a long, lighter one with a solid face. For swing gates, size each leaf on its own, from hinge centre to the closing edge, along with its weight.
Most swing gate motors publish a maximum leaf length and a maximum leaf weight. Treat both as limits you must stay inside, not only the weight figure. As a typical example, one residential swing operator range published in Australia lists a maximum of 4.5 m and 450 kg per leaf, which shows how both numbers sit side by side. Check the specifications of the exact model you are considering.
Single versus double swing
A double swing gate splits the opening into two shorter leaves, so each leaf is easier to automate than one very long single leaf. That is one reason wide driveways often suit double gates. But two leaves mean two motors, and the leaves must open and close in a set order, usually with a delay so they do not collide. Post strength, hinge quality and the space to swing all matter. Our guide to double or single swing gate checks explains how we weigh up the choice on site.
Posts and hinges
A swing operator pushes against the post as well as the gate. Weak, undersized or loose posts flex, throw off the limits and loosen fixings over time. Check that posts are solid and set properly in concrete, and that hinges are heavy duty and greased. Check that the gate swings freely by hand first. If the leaf opens into a slope or must swing outward over a footpath, tell your installer early, because both change the hardware.
Wind and the gate's face
Wind load is an invisible factor that surprises many owners. Two gates with the same weight and length can put very different loads on a motor depending on their infill.
| Gate face | Wind behaviour | Sizing effect |
|---|---|---|
| Open pickets or spaced slats | Wind passes through | Lowest wind load |
| Wrought iron with decorative panels | Moderate resistance | Allow a margin |
| Solid sheet, privacy cladding or tight boards | Catches wind like a sail | Size up, especially for swing gates |
Swing gates are more exposed than sliding gates, because a wind gust pushes directly against the opening or closing arc. If your property sits on an exposed rise or on a corner, size with that in mind. Solid privacy gates on exposed Victorian sites are a case where we generally move up a motor size or change the design, for example by adding gaps or choosing a sliding configuration.
Duty cycle: how often the gate runs
Weight and length tell you how hard the motor works on each cycle. Duty cycle tells you how often it can do that before it needs to rest. Motors are rated for a certain share of running time, and some residential operators are limited to a set number of operations a day. A family gate that opens a few times a day is a very different job from a shared entry used dozens of times an hour.
Think about your peak, not your average. A site that sees 10 movements across the day but five in the same 15 minutes in the morning puts the motor under more heat stress than the daily total suggests. Consider these cases:
- Single household: low frequency. A well-matched residential motor with a sensible margin is normally enough.
- Multi-dwelling or shared driveway: many users, bunched movements. Size up for duty cycle and choose a motor built for heavier use.
- Commercial and industrial sites: frequent cycles, often heavy gates and sometimes 24-hour use. These need industrial-grade motors and often a controlled access system, as covered on our commercial and industrial gates and automation page.
A long, high-use gate with a small motor is the classic combination for burnt-out motor boards and stripped gears.
Power supply and cable runs
Most modern gate motors run on 24 V DC, fed from a transformer and control board. That is safe and efficient, but it makes cable length and thickness important: a long run from the transformer to the motor can drop voltage under load, which can look like an undersized motor. A motor that struggles at the far end of a long driveway may need a thicker cable or a relocated power supply, not a bigger motor. We explain this in gate motor power and 24 V voltage drop.
Solar is an option where mains is far away. It needs a motor and battery sized to your daily cycles, which is another reason to know your duty cycle before you choose.
A worked example
Here is how we would think through a typical Melbourne-suburb job.
The site: a 4 m opening, sliding gate, powder-coated steel frame with vertical slats, used by a household of four plus occasional deliveries.
- Length: the opening is 4 m, plus a tail, so the gate panel is noticeably longer than 4 m.
- Weight: the fabricator's material list, or a weigh-in, gives a figure for the whole panel.
- Condition: new track, level ground, free rolling by hand.
- Wind: slatted infill, low wind load.
- Duty: a few cycles a day, low peak.
- Decision: a motor rated clearly above the gate's weight, with a safety margin for length, rather than one that just meets the number.
Now change one thing: the same gate is clad in solid sheet for privacy and sits on an exposed corner block. A sliding gate handles wind better than a swing gate, but the added weight and the sail effect on the track and rollers still raise the demand. That moves us up a motor size and makes us look closely at the roller and track hardware.
The point of the example is the order: gate, condition, wind, usage, then motor.
Upgrading an old gate motor
If you are replacing a motor, do not simply copy the old model. Gates change over the years: tracks wear, hinges sag, posts shift and usage grows. A motor that struggled before may have been undersized from the start, or the gate may have deteriorated. See upgrading an old gate motor for what to check before you buy a replacement. If your current gate has odd faults, six quick checks to tell mechanical from electronic faults can save you from replacing a motor that is not the problem.
Perspective: why we over-specify the margin
We have built and installed gates across Victoria for more than 30 years, and the faults we are called to most often trace back to sizing and setup, not to a faulty motor. A motor that is just big enough on the day of installation is not big enough two years later, once the track has collected grit, a hinge has sagged or the family has grown and uses the gate twice as often.
Because we design and handcraft our gates in-house, we know what each one weighs before the motor is chosen. That removes the biggest guess from the process. We would rather specify a motor with real headroom and have it run cool and quiet for years than save a little at purchase and be back for a repair.
The second thing we hold to: fix the gate, then size the motor. A heavy, binding gate is a fabrication or installation problem, and the honest answer is to correct it, not to overpower it.
— Rhys
Safety and compliance in Australia
Sizing is not only about performance. An oversized or badly set-up motor can push with more force than is safe, so the motor's force settings, safety sensors and stopping behaviour all need to be set to suit the gate. Our overview of automatic gate safety standards in Australia sets out what applies, and gate safety sensor questions to ask your installer helps you check an installer's work. Wiring of mains power to the transformer must be done by a licensed electrician.
For commercial sites, the workplace safety side matters too. Under the model work health and safety framework, businesses that run workplaces must eliminate risks to health and safety or, where that is not reasonably practicable, minimise them so far as reasonably practicable. In Queensland, guidance also says that anyone supplying second-hand plant must give written notice of its condition, including known faults, and verify its safety features meet current requirements. That is a good reason to be wary of second-hand gate motors without a documented history, wherever you are. Rules differ by state, so check the regulator in your own state or territory.
Checks after installation
Once the motor is fitted, a sized and installed gate still needs to be proven. Ask your installer to walk you through these, and repeat the simple ones yourself.
- Free movement. With the motor released, the gate should move easily by hand through its full travel.
- Smooth travel. Under power, it should start, run and stop without jerking, grinding or hesitation.
- Limits. The open and closed positions should be set so the gate stops gently and does not slam into stops.
- Obstruction response. The gate should stop or reverse when it meets an obstacle. Test it with a safe object, never with a person or body part.
- Safety devices. Photocells, edge sensors and warning lights should all work, and be aligned and clean.
- Manual release. Confirm that you know how to release the gate during a power failure.
- Motor temperature. After several cycles in a row, the motor should be warm, not too hot to touch for a moment. Persistent heat suggests a sizing, load or setting issue.
Then keep it going with regular servicing. Our automatic gate maintenance guide for Victorian owners lists what to do and when to call us.
Get the sizing right with us
If you want the motor sized to your actual gate and the way you use it, we handle the whole job: design, fabrication, installation and automation. Our automation and access controls team will assess the gate, power supply and site conditions and recommend a motor with the right margin. Building a new gate? Our residential gates and fencing range is made in-house with Australian-made, locally sourced materials, so the gate and motor are matched from the start.
For wrought iron designs, you can request a design consult and we will talk through the gate and the automation together.
FAQ
What size gate motor do I need?
The right size depends on the gate's weight, its length, the wind it catches and how often it runs. Choose a motor rated clearly above the gate's actual weight, not equal to it, and size up for long gates, solid infill or busy use. An installer can confirm the figure on site.
Can I use a bigger motor to fix a heavy or stiff gate?
No. A stiff gate usually has a track, roller, hinge or post problem, and a bigger motor will strain the gate and its fixings and can push with more force than is safe. Fix the mechanical fault first, then size the motor to the corrected gate.
Does a swing gate need a bigger motor than a sliding gate?
Not always. Swing gates are sized by leaf length and weight, and are more affected by wind, so long or solid leaves can demand a lot from the motor. Sliding gates are sized mainly by weight and total length including the tail. Each type should be sized on its own terms.
How does opening frequency change the motor I need?
A motor has a limit on how much of the time it can run before it overheats. A busy shared driveway or commercial entry needs a motor built for heavier duty than a single household that opens the gate a few times a day. Think about your peak periods, not just the daily total.
Can I size and install a gate motor myself?
The sizing is only the start. The motor force, safety sensors and mains wiring all have to be correct, and mains wiring must be done by a licensed electrician. We recommend having a professional install and test the system.
Sources
- Managing the risks of plant in the workplace, Model Code of Practice (Safe Work Australia, 2021)
- Managing the risks of plant in the workplace Code of Practice (WorkSafe Queensland, 2021)