Generator Power Calculator

Step 1: Getting the power information for your appliances

Determine the running (continuous) watts and starting (peak) watts needed for each appliance. In some instances, these will be the same – this is the case for appliances such as TV’s, lights and laptops whereby the starting and running wattage is the same.

But in lots of other instances (i.e. appliances that have electric motors or heating elements) the starting wattage can be multiple (3-4 times or more) of the running/continuous wattage. Examples of these types of appliances are; fridges, air-conditioners, microwaves, electric deep fryers, coffee machines, hair dryers, pumps, drills, grinders, saws etc. These appliances have motors, compressors or heating elements that will surge to a peak power demand then drop back down to a lower running/continuous amount.

So where applicable, it is very important you obtain the starting wattage for your appliance, because if your appliance(s) draw more power when surging than the generator can produce, then you won’t be able to run your appliances.

Note that often the important starting wattage amount isn't always stated in the product manual or on the product data plate, so you may need to contact the appliance manufacturer or use a wattage meter to get the right starting/peak wattage amount.

Step 2: Making sure the power information is represented in Watts (W)

If your appliance power information is represented in Amps (A), Kilowatts (kW, kVA), or Horsepower (HP), then you will need to convert these figures to Watts (W); refer to the following Power Reference if needed;

Power Reference Table

Amps Converted into Watts
1 x Amp = 240 watts

Note: this is for AC Single Phase power. Three Phase Power runs at 400 - 415 volts

HP Converted into Watts
1 x HP = 746 watts
kW Converted into Watts
1 x kW = 1000 watts
kVA Power Factor Converted into Watts
kVA = kW/Power Factor Between 0 and 1


Step 3: Work out how many appliances will you be running at any one time

If you are only running one appliance from your generator, then simply use the wattage information you have obtained from the above steps and choose a generator size accordingly.

A couple of examples;

  • Your Caravan Air-conditioner draws 2300 watts at start up and drops back to 1000 watts continuous. You opt for a Yamaha EF2400iswhich produces 2400 watts at peak and 2000 watts continuous…a good fit for your Caravan air-con unit.
  • The Water Pump on your farm draws 30 Amps (7200 Watts) to start up and then drops back down to 1800 watts to keep running. You opt for an 8kVA Powerlite Generator which can handle up to 8000 watts at peak; this is the most popular trade and farm generator.

But what if you want to run multiple appliances from your generator at the one time? There are few different things to consider in this situation. Firstly, we’ll take a look at a simple example;

  • Again, you want to run your Caravan Air-conditioner and some other small appliances as well:
Appliance  Running Wattage Starting Wattage
Caravan Air-Conditioner  1000 2300
 TV  200  0
Mobile Phone/Tablet  100  0

Simply add the highest starting wattage number (2300 watts) to the wattage sum of the other two appliances, i.e. 2300 + 200 +100 = 2600 watts. In this instance you choose a Yamaha EF2800iS which produces a peak power of 2800 watts and rated output of 2500 watts.

The above example is quite basic as there is only one appliance that surges at start up. Let’s take a look at an example of running multiple appliances with surge power requirements as there are a couple of ways to approach it. An important note here is that to maximise the generator potential, the appliance with the largest starting wattage should be started on its own first and then further appliances connected thereafter. Example;

  • After a storm in your area there is a blackout and you need to run some home appliances
  • Appliance  Running Wattage  Starting Wattage 
    Fridge/Freezer   400 1280
     Water Pump  300 1100
     TV  200  0
     Lights  60  0
     Laptop  120  0

You could choose a 2000w generator, as the highest starting wattage appliance (Fridge/Freezer) is 1280 watts and the sum of the running watts of the other appliances is 680 watts, so; 1280 + 680 = 1960 Watts. You would start first with connecting your Fridge/Freezer, then incrementally add your other appliances.

However, if the two appliances with starting wattage requirements (Fridge/Freezer and Water Pump) both surged at the same time this would require 2760 Watts (1280 + 1100 + 200 + 60 + 120), then the 2000w generator would not produce enough power. It would trip the overload circuit breaker and stop producing power. Therefore if you wanted to run multiple appliances at the same time that have surging power requirements and their peak power demand will coincide, then you will need to choose a generator size that can handle the sum of the peak demands at any one time plus the sum of the running wattages for the remaining appliances. If this is the case, then you would need a generator that could produce above 2760 Watts.

Wattage Estimation Table