Match your appliances to the right generator size, understand why starting watts matter more than the headline number, and avoid the sizing mistake that leaves Australian buyers stranded at camp or out of pocket.
More Australians than ever are buying a generator for the same two reasons: to stay powered off-grid, and to keep the essentials running when the grid goes down. The hard part is no longer finding a generator. It is working out which size you actually need.
The confusion usually starts on the spec sheet. Almost every listing quotes two wattage figures, a higher maximum output and a lower rated output, and most buyers fixate on the bigger number. The result is predictable. People either overspend on a unit far larger than their load, or they buy too small, plug in a caravan air conditioner, and watch the generator stall on startup.
This guide fixes that. We map four real output classes, the 1.2 kW, 2.0 kW, 3.5 kW, and 4.2 kW Gentrax inverter generators, against the appliances each one will genuinely run. The figures here come from the actual products we sell, not generic estimates, so you can size your purchase against your own gear before you reach the checkout.
Starting Watts Decide What You Can Run, Not the Headline Number
Every generator carries two output ratings, and the gap between them is where most sizing mistakes happen. The rated output is the power the unit can sustain continuously. The maximum output is a short surge it can deliver for a few seconds. You size to the rated figure for the load you want to run all day, but you also need enough surge headroom to cover the moment an appliance switches on.
That startup spike is the part buyers forget. Anything with a motor or compressor, like a fridge, an air conditioner, a power tool, or a water pump, draws two to three times its running wattage for the split second it kicks in. A fridge that runs on 200W can demand 600W or more to start. Plug it into a generator with no surge margin and the overload protection trips.
Across the Gentrax range, the two numbers line up like this:
- Gentrax GT1200 (1.2 kW class): 1.2 kW maximum, roughly 1 kW continuous. Built for light electronics and charging, not motors.
- Gentrax GT2000 (2.0 kW class): 2.0 kW maximum, 1.7 kW rated. Enough continuous power for a portable fridge plus lights and devices.
- Gentrax GT3500 (3.5 kW class): 3.5 kW maximum, 3.0 kW rated. Comfortable headroom for a caravan air conditioner on startup.
- Gentrax GTX4200 Pro (4.2 kW class): 4.2 kW maximum, 3.5 kW rated, and parallel capable if you later need more.
Here’s what one of our customers said about the GT2000:
“Neat compact unit, filled it with oil and fuel, started a second pull. Runs like a dream and is nice and quiet.”
The practical rule is simple. Add up the running watts of everything you want on at once, identify the single appliance with the highest startup surge, then choose a generator whose rated output covers the total load and whose maximum output absorbs that biggest surge. Browse the full inverter generator range with both figures listed on every product so you can check this at a glance.
Each Output Class Is Built for a Different Kind of Trip
Once you understand the two numbers, the four classes sort themselves into clear use cases. Here is what each Gentrax unit comfortably runs, based on its real specifications.
- 1.2 kW, the GT1200, for charging and the basics: At 1.2 kW peak and around 1 kW continuous, the GT1200 runs phone and laptop chargers, LED camp lights, a small TV, a fan, and a CPAP machine. It will not start a fridge and air conditioner together. Quiet at 58dB and light enough to carry one-handed, it is the best companion for a minimalist setup or as backup for sensitive electronics. Priced at $469.
- 2.0 kW, the GT2000, for the weekend camper: The GT2000 delivers 2.0 kW maximum and 1.7 kW rated from a 100cc four-stroke engine, with a 4.1L tank giving up to 6.1 hours of run time. That adds a portable fridge, a microwave used briefly on its own, and lighter power tools to the GT1200 list. At 18.5kg with two AC outlets, it suits caravanners running a few appliances rather than a full rig. Priced at $649.
- 3.5 kW, the GT3500, the all-rounder most people buy: The GT3500 steps up to 3.5 kW maximum and 3.0 kW rated, enough to start a caravan air conditioner up to 2.5hp (about 2,000W), keep a 400 to 600L household fridge or freezer running, and charge devices and drive power tools up to 2,500W. A 5.7L tank gives up to 4.1 hours at half load, and eco mode stretches that further. At 28kg, it is still genuinely portable. Priced at $899.
- 4.2 kW, the GTX4200 Pro, for the fully loaded rig: The GTX4200 Pro runs 4.2 kW maximum and 3.5 kW rated, so it can hold an air conditioner, fridge, and microwave at the same time, plus a washing machine or water pump. An 8.8L tank gives about 6.8 hours continuous; it offers key, remote, and pull start, and it is parallel-capable for even bigger demands. Priced at $1,449.
Run the Numbers Before You Buy: A Worked Example
The fastest way to land on the right size is to total your real load. Take a common caravan setup heading away for a long weekend in summer, with everything a family actually switches on at once.
| Appliance | Running watts | Startup surge | Notes |
|---|---|---|---|
| Caravan air conditioner (2.5hp) | ~2,000W | ~3,000W | Biggest surge |
| Portable or caravan fridge | ~200W | ~600W | Compressor |
| LED lights and fan | ~150W | ~150W | Steady |
| Phone and laptop charging | ~150W | ~150W | Steady |
| Total | ~2,500W | ~3,400W peak |
Figures are typical averages; check your own appliance ratings, which vary by model.
That load runs at roughly 2,500W continuous but peaks near 3,400W the instant the air conditioner starts. The GT2000 cannot hold it, and even a generator rated at exactly 3.0 kW would be cutting the surge fine. This is the classic case for the GT3500, whose 3.5 kW maximum absorbs the spike while its 3.0 kW rated output carries the steady load. Drop the air conditioner and the GT2000 copes easily; add a washing machine or a second high-draw appliance, and you want the GTX4200 Pro.
Whatever your total, add a 20 to 30 per cent buffer. Generators run more efficiently and last longer when they are not pinned at full output, and the buffer covers the appliance you inevitably add later.
Output tells you what you can run; the fuel tank tells you how long. Tank size and run time vary widely across the range, so factor it into your decision. The GT2000 holds 4.1L for up to 6.1 hours, the GT3500 holds 5.7L for about 4.1 hours at half load, and the GTX4200 Pro holds 8.8L for roughly 6.8 hours of continuous running at 50 per cent load as well. Eco mode on all models lets the engine throttle back to the load, which both saves fuel and drops the noise level, so a unit that idles down between fridge cycles overnight will easily outlast its headline figure on a light load.
Three sizing mistakes account for almost every unhappy return:
- Sizing to running watts only: Forgetting the startup surge is the most common cause of a generator that trips the moment the air conditioner or fridge compressor kicks in. Always size the maximum output to your biggest surge.
- Buying on price alone: A unit one class too small never feels like a bargain at camp. It is cheaper to buy the GT3500 once than to replace a GT2000 that cannot hold your load.
- Ignoring how you will use it: Remote and electric start, an LCD run time display, and parallel capability, all on the GTX4200 Pro, matter far more for a permanent caravan rig than for an occasional weekend away, where the lighter pull start GT2000 is the smarter buy.
Here’s what one of our customers said about the GT3500:
“Happily running 240V fridge and aircon on eco mode for three days, and it was 37 degrees.”
Quiet, Certified, and Serviceable Counts as Much as Wattage
Output gets you onto the shortlist, but three things decide whether a generator is right for Australian conditions: how loud it is, whether it meets local standards, and what happens after you buy it.
- Noise that keeps you legal at camp: Most national parks allow generators under 65dB, the threshold for a quiet unit. The GT1200 and GTX4200 Pro run at 58dB at 7 metres, the GT2000 at 60dB and the GT3500 at 62dB, all below that line and about as loud as a TV on low volume. Always confirm the rules with the park authority, but the range sits on the right side of the limit.
- Certification that matters here: Every Gentrax unit is EURO 5 emissions-certified, RCM-approved to Australian standards, and US EPA-tested. On top of these, it produces pure sine wave power that is safe for laptops, TVs, and other sensitive electronics.
- Weight you can actually move: At 28kg, the GT3500 weighs roughly half what other 3 kW units do, and a fraction of the price.
That last point is worth seeing side-by-side, because the premium brands cost four to five times as much for less rated output:
| Spec | Gentrax GT3500 | Brand A | Brand B |
|---|---|---|---|
| Max / rated output | 3.5 / 3.0 kW | 3.0 / 2.8 kW | 3.0 / 2.8 kW |
| Weight | 28 kg | 59 to 61 kg | ~67 kg |
| Price (AUD) | $899 | $4,070 to $4,599 | $4,360 |
Comparison figures as published on the Outbax GT3500 product page.
After-sales support closes the loop. Gentrax generators ship fast from a Sydney warehouse with free delivery to most metro areas, carry a full Australian warranty under Consumer Law, and come with a 60-day money-back guarantee. Common spare parts, fuel filters, carburettors, and ignition modules are stocked online, so a unit bought today is still serviceable years down the track. More than 60,000 have sold across Australia since 2010, and the GT3500 variant has been voted best generator every year since 2018.
How to Choose and Where to Start
Sizing a generator comes down to three steps: total the running watts of everything you will run at once, find the appliance with the biggest startup surge, then pick the class whose rated output covers the load and whose maximum output covers the surge, with a 20 to 30 per cent buffer on top. For most caravanners and home backup buyers, that points to the GT3500; lighter setups suit the GT1200 or GT2000, and fully-loaded rigs want the GTX4200 Pro.
Compare all four side by side, with full specifications and verified reviews on every listing, in the Outbax inverter generator collection. Still unsure which size fits your gear? Reach out to our team, and we will size it with you before you buy.
