Our steep driveway and farm and smallholding guides both cover how terrain and scale change motor selection. This article is different — it's about the sizing maths that applies to every gate regardless of terrain: how much your gate actually weighs, how long it is, and how exposed it is to wind, and how those three numbers translate into a motor class and torque rating on a spec sheet. Getting this step right before you buy is what our installation mistakes article deals with after the fact — that article covers spotting an undersized motor once it's already fitted; this one is about not ending up with one in the first place.
Why Weight Comes Before Gate Type
It's tempting to shop by gate type alone — "I need a sliding gate motor" or "I need a swing gate motor" — but type only narrows the mechanism, not the size. Within sliding gate motors alone, entry-level models are commonly rated for gates up to around 300-400kg, mid-range residential units stretch to 500-600kg, and heavy-duty or commercial-class motors are built for 1,000kg and beyond. Buying the right mechanism type with the wrong weight rating is one of the most common sizing mistakes, and it's invisible on the showroom floor because an undersized motor will still open the gate on day one — the problem only shows up as accelerated wear months later.
Torque, Explained Without the Engineering Jargon
Torque is simply the rotational force a motor can apply to move your gate, and it's the number that actually matters more than raw motor "power" ratings on a box. A gate motor needs enough torque to overcome the gate's weight, the friction in its hinges or track wheels, and any resistance from wind or a slight incline, with a safety margin left over so it isn't working at its absolute limit on every single cycle. A motor running near its torque ceiling constantly will feel fine when new but will show its strain first — via slower cycle times, warm housings, and more frequent thermal overload trips on hot days — well before it fails outright.
Duty Cycle: How Often the Motor Can Run
Duty cycle is the second number worth understanding, and it's often overlooked entirely. It describes how much continuous running a motor is designed for before it needs to cool down, and manufacturers usually express it as a percentage of run-time per hour or as a maximum cycles-per-day figure. A residential household with two cars and occasional visitors might only need a handful of cycles an hour at busy times, comfortably within a light or standard-duty motor's rating. A shared driveway, small business premises, or a gate used by multiple households needs a higher duty-cycle class regardless of how light the gate itself is, because the motor is being asked to work far more often, not necessarily harder per cycle.
| Motor duty class | Typical gate weight range | Typical use case |
|---|---|---|
| Light residential | Up to 300-400kg | Single household, low daily cycle count |
| Standard/medium residential | 400-600kg | Family home, moderate daily traffic, longer gates |
| Intensive/heavy-duty residential | 600-1,000kg | Shared driveways, estates, heavier steel or solid infill gates |
| Commercial/industrial | 1,000kg and up | Business premises, complexes, farm and smallholding entrances |
These ranges are a general guide, not a substitute for the specific rating on a given manufacturer's spec sheet — always check the actual figures for the model you're considering, and see our gate motor brands guide for how Centurion, FAAC, ET Systems and BFT structure their own duty-class ranges.
Length Matters as Much as Weight
Weight alone doesn't tell the full story. On a swing gate, a longer leaf gives the motor more leverage to work against at the same weight, since the force needed to start and stop the gate's swing increases with the distance from the hinge to the point where the motor arm pushes. On a sliding gate, a longer track means more rack length and rolling friction for the motor to overcome across the full travel distance, and a longer gate is also more exposed to any minor misalignment in the track. In practice, a long but relatively lightweight gate can need a similar motor class to a shorter, heavier one — length and weight should both be given to whoever is sizing your motor, not weight alone.
Wind Load: The Hidden Multiplier
Wind load is the factor most homeowners never think about until it becomes a problem. A solid infill gate — full steel sheeting, timber cladding, or a densely packed decorative panel — presents a large surface area to the wind, and on an exposed stand or a windy Highveld ridge that translates into real additional resistance the motor has to overcome on gusty days, over and above the gate's static weight. An open palisade or tubular design of the same weight is far less affected, because wind passes through it rather than pushing against it. If your gate has a solid or near-solid infill and your property is in an exposed, windy location, it's worth sizing up a duty class beyond what the static weight table alone would suggest.
What Happens When You Get It Wrong
- Frequent thermal overload trips — the motor cuts out mid-cycle on hot days as its safety cutout protects an overworked winding.
- Accelerated gearbox and drive wear — see our motor lifespan guide for how undersizing shortens a motor's working life well below its rated cycle count.
- Slower, straining cycle times — a motor working near its limit visibly labours rather than moving smoothly.
- Warranty complications — some manufacturers can query claims where a motor was clearly used outside its rated weight or duty class, so correct sizing at installation also protects your cover.
Getting an Accurate Weight Before You Buy
The single best step is asking your gate fabricator for the actual weight on the invoice or spec sheet rather than estimating from appearance. If that isn't available, a reputable installer can weigh or closely estimate the gate on site before recommending a specific model, factoring in length and infill type alongside raw weight. Treat any online "weight from photo" guess as a starting point only — the cost difference between a correctly sized motor and an undersized one shows up in call-outs and early replacement, not on the invoice on installation day.
Frequently Asked Questions
How do I find out how much my gate actually weighs?
Ask your gate fabricator for the weight on the invoice or spec sheet — solid steel and infill panels are frequently heavier than they look. A technician can also weigh or closely estimate it on site.
Does a longer gate need a bigger motor even if it's lighter?
Often yes — length increases leverage on a swing gate and rack/friction length on a sliding gate, so a long, lightweight gate can need a similar motor class to a shorter, heavier one.
What is a gate motor's duty cycle rating?
It describes how much continuous use a motor is designed for before needing to rest, expressed as a run-time percentage per hour or a cycles-per-day figure.
What happens if I install an undersized motor on a heavy gate?
It usually won't fail immediately, but it will strain on every cycle, trip its thermal overload more on hot days, and wear out well before its rated lifespan.
Sizing a gate motor correctly is one of those decisions that's invisible when done right and expensive when done wrong. If you're unsure what class your gate needs, the safest move is getting an on-site assessment before you buy rather than sizing from a catalogue description alone.