What Size Generator Do I Need?

Choosing the right size is by far the most important factor when you are buying a new generator. The size of the generator you get will determine the types of appliances you can run. Get it right, and you'll enjoy continuous hassle-free power. Get it wrong, and you could damage the generator and the appliances.

Here's our quick guide to help you get the right size (we also recommend that in conjunction with this article, you visit our Generator Buyers Guide page which has a power calculator to help you size the right generator.


1. Which Appliances?

First, you need to determine how much power is required to run your appliances. Think about the types of appliances you want to power and make a list. Will you need to use your generator for fridges and lights during a power outage or for battery packs and laptops while camping? Is it for a construction project to run power tools? Do you want a bigger generator to run your whole home?...Remember, if you choose a generator that is too small, you won't be able to run your essential appliances. What's more, overloading the generator may lead to its breakdown as well as damage to all appliances that are using its power.

What Size Generator Do I Need?


2. Power To Start

Contrary to what you might think, you need to work out the amount of power required to not only run the appliances, but also the power required to start them. This is an important thing to remember because for many appliances, the starting output requirement can be up to three to four times greater than the continuous running power needed, and sometimes even more. So if you want to power an electric drill for instance, the drill might only require 600W to keep it running but needs 900W to start up. You can find this information within the appliance user manual or some appliances will have an information plate on the item. You can also use a wattage meter to measure the power draw of your appliances (see video example below) - Take note of this number for each appliance you wish to run at any one time. We've also included a wattage estimation table for some common appliances at the bottom of this article.

Another option you have is to contact the manufacturer of your appliance to get the important starting information - this is common practice by people who have a caravan air-con units where often the starting wattage isn't obvious on the unit; so you can call Air Command, Dometic, Coleman etc. and the technical department can advise you what size generator you require. This can also be done for welders, pressure washers, pumps, microwaves etc.


3. Add Up The Running Watts

Once you've worked out which appliances you'll be running at the same time, add up all the running watts. So for example, if you're planning to run a bar fridge (180W) with toaster (500W), TV (200W) and a portable fan (40W) at the same time, you're looking at 920W.

Some appliances, such as those with motors will need up to 3-4 times the running wattage to start up


4. Add The Highest Starting Power

Then work out which of these appliances has the highest starting power, and add that amount to the total. So if the bar fridge has the highest starting power of 600W, the total is 920 + 600 = 1520W.


5. Got The Magic Number & Go Shopping

The calculations give you the magic number - you need a generator with at least 1520W of power to run these appliances together. But we always advise people to get a generator with slightly more than you need, as you don't want to risk overloading it...so in our example a Yamaha EF2000iS model would be a good option. Without a generator that meets this magic number, you won't be able to start or run your required appliances when you need them most. So it really it worth doing the numbers!

Additionally, most generators can sustain only 80% of their maximum power for the long haul. So if you continuously push your generator to over 80% of its maximum power, you will shorten its life and risk damaging the appliances connected to it. While you don't want to go too big, make sure you get something slightly more powerful than you need.

If you need more online information helping you get the right sized generator, once again, check out our Buyers Guide which also includes helpful Power Calculator advice.

The great news is there is a huge range of generators available to meet pretty much all your size requirements! Check out our range of generators at mygenerator.com.au or you can call us on 1300 400 122 for expert advice!

Lastly, check out the below video of a customer demonstrating the use of a wattage meter to measure the power draw of his appliances -this is a good example of checking the wattage of a particular piece of equipment to make sure you get the right sized generator:-

Yamaha EF2000iS Generator Parallel Capability and Wattage Test


Wattage Estimation Table for Common Appliances

DISCLAIMER* Please note, this advice is general in nature and we strongly recommend consulting the product manual and where relevant, a professional installer.

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