How Much Generator Power Do I Need? (The Wattage Calculator)

Choosing a generator size usually comes down to avoiding two mistakes: buying a unit that is too small (so your appliances won't turn on) or buying a unit that is too large (so you waste money on fuel and carry unnecessary weight).

To find the right size, you just need to look at the power labels on your appliances and do some simple math.

Step 1: Understand Running vs. Starting Watts

Every appliance has an electrical data plate on the back or bottom. On it, you will see two numbers:

• Running (Rated) Watts: The continuous power an appliance needs to stay on. Laptops and lights draw a steady, predictable amount of running watts.

• Starting (Surge) Watts: The brief burst of extra power needed for 2 to 3 seconds just to kick an electric motor into gear from a dead stop.

Any item with a compressor or motor, like a caravan reverse-cycle air conditioner, a portable camping fridge, or a microwave, needs a lot more power to turn on than it does to stay on. If your generator can't handle that initial surge, it will instantly overload and shut down.

 

Where to Find the Data Plates

If you aren't sure where to look on your gear, check these common locations:

• Portable fridges: Usually on a silver sticker near the compressor vent or inside the lid.

• Kettles and blenders: Stamped directly onto the plastic underneath the power base.

• Microwaves: Always have a large safety label on the back panel.

The "Hidden" Labels: What if it only shows Amps?

Many appliances in Australia only list "Amps" (A) and "Volts" (V) instead of Watts. If your appliance doesn't state the wattage clearly, you can find it using a simple conversion formula. Since Australian mains power is a standard 240V, multiply the listed Amps by 240 to get the running watts:

Watts = Amps x 240V

For example, if a portable appliance label says it draws 5 Amps, its power requirement is 1,200 Watts (5A x 240V)

Step 2: Use the 3-Step Math Formula

To find your minimum generator size, write down the numbers for the items you want to run at the same time, then calculate:

1. Add up all the Running Watts of those items.

2. Find the highest single Starting Watts requirement on your list.

3. Add those two numbers together.

You don't need to add up all starting watts because your appliances rarely turn on at the same fraction of a second. You only need to account for the single biggest hurdle.

Total Generator Capacity Required = Sum of All Running Watts + Highest Single Starting Watts Surge

Real-World Example:

If you want to run a mobile fridge (150W running / 300W starting) and charge a laptop (60W running / 60W starting) at the same time:

• Total Running Watts: 150W + 60W = 210W

• Highest Starting Surge: 300W (from the fridge)

• Total Capacity Needed: 210W + 300W = 510W

Quick Wattage Reference Guide

Here is a breakdown of what common camping and household appliances typically draw:

Step 3: Match Your Total to a Real Generator

Once you have your total wattage number, look at how our specific inverter generators fit your real-world needs.

The Light Camping Setup (2kVA – 2.4kW Capacity)

If you only need to keep food cold, charge phones or laptops, run basic lights, and occasionally use a microwave or CPAP machine, a small suitcase-style unit is plenty.

The Cromtech Outback 2.4kW Inverter Generator handles these exact camping essentials easily. It gives you enough power for a standard weekend away without taking up too much space in your vehicle.

The Full Caravan Setup (3kW – 3.5kW+ Capacity)

If you want to run a built-in caravan reverse-cycle air conditioner, boil a standard kitchen kettle, or use a hair dryer, a small generator will trip.

Air conditioners need a huge starting surge to kick the compressor over. For this setup, you need a heavy-duty option, such as the iTechWorld RedBack RB3.5 3500W Portable Inverter Generator. It provides the extra muscle required to handle those big motor surges without cutting out.

The 80% Rule for Your Engine

Never run a generator at 100% maximum capacity for hours at a time. If a machine is rated for 2400W continuous output, running it at exactly 2400W for half a day strains the engine and burns fuel fast.

For the best fuel efficiency and to make your machine last longer, try to keep your continuous load at around 80% of what the generator is rated for. Keeping that 20% safety buffer ensures your generator runs quieter and stays reliable when you are far away from help.

Real Buyer Questions About Sizing

Can I link two small generators together to get more power?

Yes, most modern inverter generators feature parallel capability. If you already own a 2kVA unit and need to run a caravan air conditioner, you can connect a second matching unit using a parallel cable kit. This links their outputs together to double your capacity without requiring you to buy or lift a single heavy, industrial machine.

Does altitude or heat change how much power a generator produces?

Yes. Generators lose roughly 3.5% of their total power capacity for every 300 meters of elevation above sea level, and about 1% for every 5.5°C above a standard outside temperature of 25°C. If you are caravanning through hot regions like the Top End or parts of the Outback in peak summer, always size your generator with a slightly larger safety buffer.