You’ve decided to buy a generator for camping, tailgating, or powering your house. Then the all-important question of generator shopping hits you; “how big of a generator do I need?” You need to invest your hard-earned cash in a generator that is big enough to power your refrigerator, central AC, MIG welder, air compressor, and any other electrical appliance you have.

Unfortunately, finding the right size generator is not as straightforward as you may think. There are hundreds or even thousands of models ranging from standby models that can power an entire apartment to portable recreational units that can only power an RV. This makes the decision rather daunting. To find out how to choose the best generator for your needs, read on as we highlight a simple DIY technique.

Importance of Choosing the Right Size Generator

First things first, generators are not sized based on their physical dimensions! The size of a generator is actually a measure of its electrical output – i.e., watts or kilowatts. Sure, there are tons of factors to consider when planning to buy a generator, including the cost and portability – but none is as important as the size of the generator. Why so?

Too large a generator, and you’ll overpay. Too small, you’ll risk overloading the unit – and you don’t want to know what follows (PS: Appliances get fried and the generator overheats). Below are a few advantages of nailing down the right size generator:

  • Minimizes the risk of asset damage
  • Boost the longevity of the generator and appliances
  • Reduced incidents of unexpected system failure
  • Improved performance and hassle-free maintenance
  • Assured personal safety
  • Value for money – you don’t overpay on the unit and maintenance

Determining the Right Size Generator – In Just 2 Steps

Please keep in mind that it’s advisable to seek the expert opinion of a certified electrician when calculating the power requirements of your appliances and the best-fit generator to power them. The DIY guidelines below are meant to get you started on the right track. Besides, “winging it” is not the best approach when all your precious appliances are at stake.

Step 1 – List the Power Requirements of your Appliance

What do you need to power? List all the items or appliances that you plan to power using the generator and determine their wattage. Wait, how do you know the power requirements of your freezer or home theatre?

It’s important to differentiate between the starting and running watts unless you want to risk overheating your small generator. Surge or starting watts refers to the power required to kick-start your electrical equipment to life. On the other hand, running wattage is the amount of power an appliance needs to function after it’s turned on.

The surge (starting) and running wattage are often indicated in the owner’s manual or identification plate on the device – and if you can’t find this information, there are wattage estimation guides for most electronics on the internet.

Keep in mind that the power requirements of some electronics are stated in amperes (Amps or A). Hence, you’ll be forced to convert the unit of measure into watts. Relax, it’s not as complicated as you might assume. All you need is the formula: Wattage = Amps x Volts. As for volts, most appliances are rated 120V as per the standard – except a few tools such as TIG welders that may run at 220V.

Step 2 – Calculate the Total Wattage

The first step is determining the total power requirements of each appliance is by adding the starting and running wattage. For example, some refrigerators have a starting wattage of 2,900 watts (indicated by the buzzing sounds of the compressor when it’s turned on) and running wattage of 800 watts. This means that your generator should supply at least 4,000 watts to power the refrigerator. But you’re not buying a generator just to power your fridge, are you?

If you’re planning to plug in multiple appliances, the general rule of thumb is to add the total running watts of all your listed devices and the highest running wattage among the devices. So, if all your devices have a combined running wattage of 15,600 watts and the highest starting wattage (e.g. of the central AC) is 8,000 watts, your generator should be rated at 24 Kilowatts.

It’s also important to determine the generator’s surge and running wattage. You may have calculated that the required running wattage of your appliances is 24kW, but does the generator run at the same wattage? Although it may be rated at 24kW surge watts, the running watts may be only 23kW – and that doesn’t cut it for your power generation needs.

Also, check this quick video tutorial on how to choose a generator size:

Final Remarks

Yes, we know – finding the right generator is a pain, especially when you don’t have a clue on what to look for. Luckily, this guide should help you determine the right size to power your house without the risk of overheating or overpaying for a unit. You now only need to worry about the cost, portability, noise level, and eco-friendliness, among other factors.

Aside from the calculation of power requirements, it’s also essential to determine the power outage scenarios that may influence how big of a generator you need. Ask questions such as: How frequent are the power outages? Are they occasional, rare, or a common occurrence? With this information, you can confidently walk to your dealer, ready to make an informed purchase decision.