What size Generator

What Size Portable Generator Do I Need?

What size Generator : The most important decision you make when Choosing a Generator is making sure the genset can handle all your power requirements. If your Portable Generator doesn’t provide enough electrical output to power up your appliances, this can damage not only your appliances, but the generator as well.

Choosing the right generator can seem confusing to the untrained eye. Do I need Single Phase, Three Phase, AVR or brushless alternator? It doesn’t have to be that difficult…

These days Portable Generators are available in a wide range of sizes from 800w to 3 megawatts. Portable generators are used every day, by millions of people around the world, for many different applications. Be they for: Recreational, Domestic, Trade related or Industrial requirements.

When shopping for a Portable Generator, the first and most critical factor you need to determine is the amount of power required to not only run the appliances you wish to use, but also the power required to start them.

For example, the starting power requirement can be up to 3 times greater (or more) than the continuous running power needed. Ie. In the case of an Electric Drill the starting power might be 900W, but it only requires 550W to keep it running (you can find this information located in the appliance user manual and/or identification plate, or if not displayed there, you can use a wattage meter to check the draw of your appliances – see video below).

Yamaha EF2000iS Generator Parallel Capability and Wattage Test

It is critically important that you know the specific wattage requirements of the appliances you intend to run off the generator.

If you base your purchase decision solely on quality or price without any other consideration you may be sadly disappointed. It is far better to spend the time to determine your power generation requirements before making a choice.

To do this you need to;

  1. Develop a list with all the appliances you intend to power up off the generator at any given time.
  2. Make a note of the starting and running wattage of each appliance. The starting power is the most important factor as it can be several times that of the running power. (as a guide, see the wattage estimation table at the bottom of this article)
  3. Determine which appliances will be running at the same time. Calculate the total ‘Running Watts’ amounts for these appliances. Then determine which of your appliances has the highest ‘Starting Power’. Add that amount to the total.

i.e. Three appliances with a total running power of 1160W:


Running Power

Starting Power

Portable Fridge



Small Toaster












(These wattages are examples only, remember to check the identification plate or manual on your appliances for exact starting and running wattage)

From this table you can see that the appliance with the highest starting wattage is the toaster, requiring 750W. Then add the highest starting wattage to the total running power of all the appliances:

750W + 1160W = 1910W

From this calculation you know that you need a Generator with an output of 1910W or more to run these appliances together. It’s advisable to have a Generator with slightly more power than you need as it’s better to be safe than sorry. In this example, a Yamaha EF2000iS or an Yamaha EF2400iS would be the perfect choice.

What size generator do I need?

If your generator doesn’t have the right amount of power, then you won’t be able to start or run those appliances when you need them most.

Tradesman Generator on site

Take a few minutes and do the calculations so you know what power generator you need. If you can’t find the user manual for you appliance, you should be able to find out the information online.

There are many benefits to Choosing a Generator with the right amount of output:

  • No system failures due to capacity overload
  • Increased lifespan of the generator
  • Guaranteed performance
  • Increased safety
  • Lower maintenance costs
  • Reduced risk to asset damage

There are numerous factors to consider when selecting the right generator for the job. For more information see our Generator Buyers Guide or Contact Us today. The team at My Generator will be more than happy to assist.

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

Sean Connolly

Sean is the co-founder and Director of My Generator (mygenerator.com.au) with a keen in interest in the outdoors and power products.

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15 thoughts on “What Size Portable Generator Do I Need?”

  1. Hi and thanks for your informative post. I wish i’d seen this before I bought my last diesel generator… Unfortunately it was under size for most of my jobs around the farm. I’ll follow your advice do the calcs and check out your range. Many thanks, Simon.

  2. Thanks for sharing this informative post. When buying a generator it is best to first know how much power your applicances will consume. From that you have a guide as to what generator size you are going to need.

    1. Thanks for your comment Nancy!
      That’s spot on – It’s definitely best to know how much power all your appliances will draw and start up and continuous. From this calculation you will be able to choose a generator that will produce enough power to start and run all your appliances.

  3. Hello Sean,

    Thinking about buying a Lectron 2000w Inverter Generator as I’m about to build a shack on our bush block. It would need to run a concrete mixer, power saw, drill and maybe a couple of other things. We are in no mad rush to get the shack built so running only one tool at a time wouldn’t be an issue if it meant less stress on the generator. We would then use it to run lights, radio, kettle, etc. once the shack is in use. Would this Lectron do the job?



    1. Hi Joe,
      Thanks for your inquiry. In order to be sure that any generator can run the appliance you want to, you need to find out the exact wattage requirements of that appliance. This can found on the data plate on the item, or within the product manual. Many tools will have a peak starting wattage and a running wattage, so you’ll need to check for both. We have a guide that shows you how to calculate the wattage for different appliances here: https://www.mygenerator.com.au/generators-buyers-guide/
      This will help you decide whether a 2000w generator is enough power or not.
      Thanks again,

  4. I need to run 4 roasters [1100 watts/110 volts is approximately 13 amps per roaster] in a food booth. Do all portable gensets com with amp breakers? I saw one that had a breaker rated at 14 amps. This would let me operate only one roaster at a time. Do I get one at 4400 watts and the ability to handle 45 amps or do I get 4 to handle all 4 roasters individually because of the amps?

    1. Hi Ed – we frequently sell generators for this type of food business. Perhaps the best thing to do is give us a call on 1300 400 122 to talk through your particular roaster wattage details; Australian appliances run at 230/240 volts so we’ll need to make sure we get the wattage calculation right so we can recommend the right sized unit(s) for you. We look forward to your call – cheers!

    1. Hi Brian, it depends on your application. For example, a portable inverter generator has the ability to idle up or down depending on the load required. These a very popular for caravan/camping applications, small home backup power, and small mobile businesses such as food trucks. This idle feature makes invetrter generators very fuel efficient and quiet. The drawback with portable inverter generators is that they are more expensive and are only available in sizes up to around 7-8kVA.
      A conventional generator does not have this idling feature and therefore it is not as economical. However, portable conventional generators are popular for trade and worksite applications where running larger tools/machinery with heavy inductive loads is required. Portable conventional trade generators are built tough and range from around 3kVA to 16kVA in size.

  5. Hi Sean, this was an awesome blog! Really enjoyed it. I came across it as I was doing some research for a blog I was writing for the company I work for; Makinex Construction Products. I look forward to reading your pressure washer blogs. Cheers, Georgia

  6. Hi There
    I am wondering what you do about about having a ten amp outlet on the generator but a 15 amp inlet on the caravan.
    Obviously not allowed an extension cord with 10 amp one end a 15 amp the other end.

  7. Hello there I want to run a 2000watts 9inch angle grinder and not sure what generator will I need, could you please help me with this.

    Many thanks,


    1. Hi Alex, as a guide we would say that most angle grinders have a start up requirement of around 3-4 times the running power. In your case this would be approximately 8000 watts therefore I would suggest you look at one of our 8kVA Honda Powered Petrol Generators including:

      Powerlite Honda 8kVA Generator
      Gentech Honda 8kVA Generator

      These are Australian assembled units designed for the worksite.

      If you would like to discuss further, feel free to call our product expert team on 1300 400 122. Thanks

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