Buying a generator without knowing what size you need is like buying shoes without checking your feet. You might get lucky, but chances are you will end up frustrated. The most common mistake Australians make when shopping for an inverter generator is guessing their wattage needs instead of calculating them.
Whether you are preparing for blackouts at home, powering a caravan air conditioner on the road, or keeping the essentials running at a campsite, the right generator size depends entirely on what you plan to plug in. This guide breaks down exactly how to work out your requirements and match them to the right Outbax Gentrax model, so you spend once and get it right.
How Generator Wattage Works: Rated, Maximum and Starting Watts Explained
What Is the Difference Between Rated and Maximum Wattage?
Every inverter generator has two wattage numbers: rated (or continuous) and maximum (or peak). The rated figure tells you what the generator can sustain for hours at a time. The maximum figure is the short burst capacity the unit can handle for a few seconds during startup surges.
When sizing a generator, always base your decision on the rated wattage. If a unit is rated at 3,500W, such as the Gentrax GT3500, and has a maximum of 4,200W, treat 3,500W as your working limit.
Why Starting Wattage Matters for Motors and Compressors
Appliances with electric motors, including fridges, air conditioners, and water pumps, draw significantly more power in the first few seconds of startup than they do when running. A caravan air conditioner might run at 1,500W but needs 2,800W to kick on. If your generator cannot handle that initial surge, the unit will either trip its overload protection or fail to start the appliance at all.
Cold King 12v Rooftop Air Conditioner
kW vs. kVA: Which Number Should You Trust?
You will see some generators listed in kilowatts (kW) and others in kilovolt amperes (kVA). For most household and caravan applications, these numbers are very close. A pure sine wave inverter generator typically operates at a power factor near 1.0, meaning 3.5kVA is roughly equal to 3.5kW. If the manufacturer provides both figures, use the kW rating for your calculations.
What Size Generator Do You Need for a House?
Common Household Appliances and Their Wattage Requirements
Getting a clear picture of your home’s power needs starts with listing what you actually want to run during an outage. Here are typical running wattages for common Australian household items.
A standard fridge draws around 150W to 200W. LED lighting across several rooms sits at roughly 100W to 200W total. A modem and router together pull about 30W to 50W. A microwave typically runs at 1,000W to 1,200W. A portable fan uses about 50W to 75W. A television draws roughly 80W to 150W, depending on size.
Calculating Your Total Home Backup Load
Add up the running wattages of every appliance you want to power simultaneously. Then check which of those items has a motor and factor in its starting wattage. Your generator’s rated capacity needs to exceed your combined running load, and its maximum capacity needs to cover the highest starting surge.
For example, running a fridge (200W running, 600W starting), LED lights (150W), a modem (40W) and a TV (120W) gives you a running total of 510W with a peak surge of roughly 910W when the fridge compressor kicks in.
Gentrax GT2200 Pro Inverter Generator
Recommended Inverter Generator Sizes for Home Use
For light home backup covering essentials like a fridge, lights, and charging devices, a generator rated at 2kW to 3.5kW handles the job well. The Gentrax GT3500 Inverter Generator is a strong option here, offering enough rated capacity for everyday essentials with headroom for startup surges.
If you want to run more demanding loads, such as a microwave, multiple fans, and a fridge simultaneously during an extended blackout, step up to the Gentrax GTX6600. This unit gives you the overhead to manage heavier household loads without straining the generator.
Here’s what one of our customers said about the GTX6600:
“After trialing 3 of them, we are launching these in all our jobsites. Surprisingly smooth and a beast of an output. Easy to start and reliable so far. If you understand generators or what this generator does, you would know this is a bargain of a price. Don’t let the low price put you off, the quality is superb! Speedy delivery every time. One of them arrived the very next day!”
What Size Generator Do You Need for a Caravan or RV?
Powering a Caravan Air Conditioner: Minimum Wattage Requirements
The single biggest power draw in most caravans is the rooftop air conditioner. A typical caravan aircon unit runs at 1,200W to 2,000W, but its starting wattage can spike to 2,500W or even 3,000W depending on the model and ambient temperature.
This means a 2kW generator like the Gentrax GT2000 inverter generator will almost certainly not start a caravan air conditioner. You need a generator with enough peak capacity to handle the startup surge and enough rated capacity to keep the unit running continuously alongside other appliances.
Gentrax GT2000 Inverter Generator
Running Multiple Caravan Appliances at Once
Most caravan owners do not just run the air conditioner. A 12V fridge (around 50W via the inverter), LED lighting (30W to 60W), phone chargers (15W to 30W), and a small water pump (100W) add to the total. With the aircon running, your combined load sits comfortably between 1,500W and 2,300W, with peak surges well above 2,500W.
The Gentrax GTX4200 Pro Inverter Generator handles this scenario with confidence, delivering enough headroom for the aircon startup and sustained capacity for everything else.
Here’s what one of our customers said:
“Great generator, just used it at an event to run the equipment on a food stand with a fridge and 2 baine maries all day and didn’t miss a beat.”
Choosing a Quiet Generator for Caravan Parks
Noise matters in caravan parks. Many parks enforce strict decibel limits, and fellow campers will not appreciate a loud generator running through the evening. If your caravan setup does not include an air conditioner and your loads are moderate, a 2.5kVA pure sine wave inverter generator, such as the Gentrax GT2500, offers a quieter inverter generator option with enough power for a fridge, lights, chargers, and a small cooking appliance.
For Outbax customers planning extended caravan trips, matching the right generator to your specific load list is more important than simply buying the biggest unit available.
What Size Portable Generator Is Best for Camping?
Typical Camping Power Needs: Lights, Phones, Fridges and More
Camping power requirements are usually far more modest than home or caravan needs. A typical camp setup might include a 12V portable fridge (40W to 60W), a string of LED lights (10W to 20W), phone and tablet chargers (20W to 40W), and perhaps a small Bluetooth speaker. The combined load rarely exceeds 200W during normal use.
Even if you add a portable kettle or a small induction cooktop for brief cooking sessions, a compact inverter generator in the 1kW to 2kW range covers everything comfortably.
When a Small Generator Is All You Need
There is no point carrying extra weight and burning extra fuel for wattage you will never use. The Gentrax 1kW Inverter Generator is purpose-built for lightweight camping, easily powering basic electronics and a 12V fridge without the bulk or noise of a larger unit.
If you want a bit more flexibility, perhaps to run a small toaster or charge a lithium battery system at the same time, a 2kW-rated unit, such as the Gentrax GT2200 Pro Inverter Generator, provides that extra margin while remaining highly portable.
Matching the Right Outbax Gentrax Generator to Your Needs
Quick Reference: Gentrax Models by Wattage and Use Case
Choosing the right generator size comes down to matching your calculated load to the correct rated capacity. Here is a straightforward breakdown.
- Gentrax 1kW range: Suits lightweight camping with basic electronics
- Gentrax 2.2kW range: Covers camping with moderate loads and small cooking appliances
- Gentrax 2.5kW range: Ideal for caravans without air conditioning, where quiet operation is essential
- Gentrax 4.2kW / 3.5kW range: Fits caravan air conditioning and moderate home backup
- Gentrax 6.0kW range: Built for heavy home backup and demanding multi-appliance setups
Gentrax GTX4200 Pro Inverter Generator
Why Pure Sine Wave Output Matters for Sensitive Electronics
Every Gentrax Inverter Generator produces pure sine wave power, which is critical if you are running laptops, medical devices, CPAP machines, or any electronics with sensitive circuitry. Modified sine wave generators can cause buzzing, overheating, or outright damage to these devices. For both home and caravan use, pure sine wave output is a non-negotiable feature.
Choose the Right Size Generator and Stop Guessing
Getting the right inverter generator size is not complicated once you know your numbers. Add up your running wattages, account for starting surges, and give yourself a sensible buffer. Whether it is a compact 1kW unit for a weekend campsite or a 5.5kVA workhorse for the house, Outbax has a Gentrax model built for the job.
Browse the full inverter generator range at Outbax and match the right size to your setup today.
