What Size Generator Do I Need?

Last Updated: August 8, 2022
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Buying a generator for your house or company is a significant investment. It’s also one that most consumers don’t make very often, so there’s a lot of confusion around which fuel type to use (diesel, gas or propane), which brands are best (Champion, Honda Generac, Westinghouse), and most importantly, what size generator is appropriate.

Before purchasing a generator, one of the most common questions people ask themselves is, how big do I need it to be? How big a generator do I need to run a fridge? Would it be able to power an entire home? What is the recommended wattage for my MIG welder, sump pump, and air compressor? what is a good size for RV?

For an accurate estimate, your first and best option is to consult a certified electrician. If you want to do it yourself, you may still buy or rent a competent generator by following some simple recommendations. We’ve laid them out for you to see so you can figure out what size generator you’ll need.

Choosing the best generator should be a delicate balancing act. To power your equipment, you’ll need enough electricity, with higher output required to run huge appliances or several tools at the same time. High-power generators, on the other hand, are more expensive to buy and require more storage space due to larger size, so there’s no point in investing in the additional capacity if you won’t need it.

Why It’s Important

If you think that the easiest thing to do is just to use a generator and start seeing if it works with your needs, doing some research and figure out what size generator you will need before using a generator will save you from a lot of unnecessary problems.

For instance, if you choose the appropriate size generator, it will perform better and last longer. It won’t suffer from capacity overloads that cause sudden system breakdowns. In addition to damaging your home’s electrical wiring, you could also damage your generator.

You’ll need to count up the total watts of anything and everything that will be plugged into a generator, and then figure out what size generator you’ll need based on the overall amount of watts.

It’s also worth noting that certain devices use more power to start than to run. When determining how many watts are required to run a tool, you should also determine how many watts are required to start the device and include that to your final wattage. It’s also a good idea to add 10% to your final total to ensure that you have sufficient power in your generator.


1. Small Generator

Once you know your total wattage, you can start looking for the best generators for your needs. Small generators can power about 1,500-2,000 watts. You might want to get one of these if you’re powering a few small appliances and appliances in your home.

This is a popular choice for people who are looking to power a few small devices and appliances in their home for short periods of time, like a fridge, furnace fan, and a few other small devices. If you’re looking for a generator to have as a backup on a job, this is a good option for you.

2. Large Generator

As these can handle between 6,000 to 9,000 watts, large generators can create more electricity. Many people choose big generators because they can supply electricity to multiple rooms in a house. Large inverter generator can also produce clean power for you sensitive electronics.

If you know you’ll need at least 6,000 watts of electricity, you should consider investing in a big generator that can power all of your equipment and appliances at the same time.

3. Extra-Large Generator

An extra-large generator is perfect for jobs where you need to use large power tools, like a drill or saw or AC. It can generate more than 10,000 watts of energy at once, so it can power a central air conditioning unit in your home along with other appliances like a fridge, pumping system, and electricity.

When choosing an generator, go with the highest wattage possible for your project If you’re not sure how much power your job will require.

Residential Vs. Industrial Generators

You already know what type of generator you need. If you are a homeowner in need of backup power, you can either use a portable generator or a stationary generator. Sizes range from 2000 watts or less for a recreational unit and up to to 50 kilowatts for a whole-house generator. These generators use a single-phase current, which is enough to power small equipment that does not need high-voltage power.

Industrial generators come in a variety of sizes, ranging from 20 kilowatts to 3 megawatts. Larger corporate and industrial applications demand more capacity and, as a result, three-phase motors with higher power are frequently used. For office buildings, manufacturing facilities, and building complexes such as shopping malls, institutions, and living centers, larger-capacity generators are required.

How To Size A Generator

The basic generator sizing formula is:

  1. Make a list of all items that will be powered.
  2. Find the starting wattage and running wattage for each piece of equipment. These figures are typically given somewhere on the equipment itself, and the owner’s manual should also have this information.
  3. When calculating your electricity consumption, add up the figures for the total kilowatt (kW) or watts or kilovolts-amperes (kVA) that you need to meet your energy demands.

For equipment rated in amps, you can convert amps to watts by using the following formula or use a calculator :

  • Wattage = amperes x volts (resistive loads)
  • Wattage = amperes x volts x load factor (reactive loads)

The load factor is the ratio of your electricity use in kilowatt-hours to your peak demand in kilowatts. You may figure it out by looking up the information on your power bill and plugging it into the formula below:

  • Total kWh last month / (peak demand for the month x 30 x 24)

The size of the generator you buy depends on your needs, but keep in mind that the larger the generator, the more expensive the generator.

Buy a generator with a capacity that is 10-20% greater than your requirements, so you’ll have some leeway when and if you decide to increase your equipment or need more power.

Generator Size & Fuel Consumption

Larger generators burn gasoline at a higher rate than smaller units, which means that a 3500cc vehicle consumes more fuel than a 1500cc.

When calculating the cost of a new generator, it’s important to know this. Not only must larger generators be refueled more frequently, but it may also be necessary to store more gasoline on-site, which necessitates the installation of additional storage tanks.

Consumer Reports suggests that you choose the smallest portable or home generator that suits your needs in order to limit the amount of fuel you have to store to run it.

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I am a mechanical engineer with years of experience working on Internal combustion engine and fixing electrical and mechanical systems, generators, transfer switches, and equipment related to storm water and sewage pumping stations.