How To Select Right Sizing Generator: A Complete Buyer’s Guide

How To Select Right Sizing Generator: A Complete Buyer’s Guide

Selecting the right size generator can be a challenging task. You’ll need enough electricity to power your devices uniformly with greater output power required to run large appliances or multiple electronic tools together. It requires more cost to purchase High-power generators, however, cost more to purchase and require more room for storage due to the larger unit size, so there’s no need to purchase extra capacity if you won’t need it. The following are some expert advice for choosing the right generator sizing to your power devices needs

Furthermore, choosing the single-phase, three-phase, kW, KVA, welder, standby or motor starting generators or AC(alternating current) and DC(direct current) generators can be struggling.

To stop such confusion, we have developed this article to help you get a better idea of how the sizing process of generator works and some key factors to keep in mind while choosing a suitable generator for your needs. We have mentioned enough information in an understandable form for the ultimate buyer. So that he can get a solid understanding of some key factors before he buys.

How the Sizing of Generators Categorized

To know which size of generator suits your requirement appropriately you should first understand how generators are sizing when manufactured.

The S.I. unit for sizing generators is watts(W) or kiloWatts(kW). Both watts and kilowatts are a measurement of electricity where 1kiloWatt= 1000 Watts.

Thus, a generator’s size has nothing to do with its physical measurement size. Its size refers to its capacity of how much electrical power it supplies for the appliances.

The side effect to choose wrong size generator according to your requirement?

A generator that doesn’t provide backup as much electricity as you need can cause a voltage drop and damage both your appliances and your generator or it will not supply power at all. But go too big and you’ll end up overpaying for the unit and the operational costs.

So let’s take a closer look at the steps you’ll need to follow to find the perfect size generator for your needs.

Types of Generators

3 types of generators exist in the market such as portable, inverter and standby. In spite of their differences in output and cost, all of these generators should undergo a common generator maintenance process to ensure effective long-term use.

Portable Generator

A portable generator is a gas or diesel-powered generator that provides temporary electrical power. However, the engine turns a small transformer which in turn provides usable electricity up to a certain level of wattage. Users can easily plug-in electrical appliances directly into the generator’s sockets, or the generator can be professionally paired into the sub-panel of a home or workplace.

Here are some characteristics of Portable Generators:

  1. Uses a combustion engine to conduct electricity.
  2. It can be plugged into electrical appliances or tools via its power sockets.
  3. These can be wired into a facility’s subpanels in apartments.
  4. It can be used in remote sites.
  5. It has enough power to run a television, freezer, and refrigerator.
  6. Use a governor to control the engine’s speed.
  7. Can power tools and lights.

Inverter Generator

An inverter generator electronically strangles the engine up and down to meet the power demand. Instead of running full time. The resulting improvement in efficiency means that you won’t have to fill it up as often. Inverter generators also produce lower radiation and are generally very quiet in comparison to the portable generator.

Here are some characteristics of Inverter generators:

  1. Relies on high-tech magnets.
  2. Uses advanced electronic circuitry.
  3. Undergoes three phases to produce electricity.
  4. Outputs AC, convert it to DC and finally invert it to AC.
  5. Maintains a constant flow of current to an appliance.
  6. It is more energy-efficient, as the engine speed adjusts itself according to how much power is needed.
  7. Its Alternating Current can set to any voltage and frequency while used with proper equipment and tools.
  8. Tends to be, little and lightweight.
  9. It can be easily fit into a car, RV or boat.

Standby Generator

However, a standby generator is an electrical system that operates with an automatic transfer switch that commands it to power a device up during power loss.

So here are some characteristics of Standby Generators:

  1. Operates automatically.
  2. While Delivers permanent power protection to the protected place.
  3. It made of two components, a standby generator, and an automatic transfer switch.
  4. So it can be operated on liquid fuel or natural gas.
  5. This will run on the fuel type already in use in the facility or home.
  6. That uses an internal combustion engine for supply.
  7. It can sense the power loss within seconds and boots up electricity so that power loss doesn’t cause any harm.
  8. Executes automatic weekly self-tests to see that it is properly reacting to a power loss.
  9. It is constantly monitoring utility power to prevent any power loss.
  10. Finally, it Used in safety systems for elevators, standby lighting, medical and fire protection systems.

Best Sizing Generator for Different Outages

Generator TypeBest Use
Portable Generator sizingRefrigerators, spray gun systems, nail guns
Inverter GeneratorCar batteries, laptops
Standby GeneratorEmergency settings, hospital machinery Generator sizing

Different Sizing Generator Available in The Market

The following table will quickly summarize how much electricity various power generators can produce for backup…

Rated WattsDescriptionDegrees of Power
5 kWThis basic system that can restore power to multiple basic survival appliances.Four lights, furnace fan, sump pump, and refrigerator/freezer
6.5 kWThis watts system is used to keep all the survival appliances also operating and a few extra tools work properly.Survival appliances in addition to the family room.
8 kWWhile this mid-Sized generator system helps you weather there are powerless days and nights.Survival appliances in addition to the family room and home office.
10 kWThis is an emergency backup power system that provides comfort and security.Survival appliances in addition to the family room, home office and kitchen.
15 kWThis is a powerful system with enough energy to run a small home for 24 hrs. And above with no power issues.Survival appliances plus family room, home office kitchen and laundry room.
25 kWIt is a mini-power plant generator that can run a small to mid-sizing home or business.All of the above plus an air conditioning system.
30 kW and upFinally, it is a mini-power plant generator that can run a mid-sized to large home or business.All of the above appliances and more. Exist in total comfort.

Note: If you need massive power supply then you can go with any renowned 15 kW to 30 kW sizing generator.

How To Determine Our Wattage Requirements

Going to a dealer for buying the best or cheapest generator available out there in the market without any other technical consideration is not the best approach. It is always better to scrabble deep into your redundant power generation requirements before making a choice. You can do this in the following ways:

  1. Make a list of the electronic appliance that needs to be powered by the generator.
  2. After that make note of the starting and running wattage needed by the respective electronic appliances.
  3. Calculate the total power requirements in K.V.A. ( kilo Volts Amperes) or KW(kilowatts)

How To Calculate Which Sizing Generator We Should Acquire

Selecting the right size generator for custom requirements (especially running watts and starting watts) depends on what you want to power and for what period. Running/rated watts, are the continuous power watts needed to keep items running with a uniform supply. Starting watts are those extra watts needed for two-to-three initial seconds to start electronic motor-driven products like a refrigerator or wood cutter machine. This at least should be equal to the maximum wattage the generator can produce.

To determine your wattage requirements:

  1. Select the electronic equipment you wish to power at the same time as the generator.
  2. List the running watts and additional starting watt requirements for each item (check your owner’s manual for each product or the data plate to locate these wattage requirements).
  3. Also, Calculate and add the running watts of all the items in the list you wish to power. You’ll need a generator that produces at least Running Watts equal to your list’s running watts.
  4. Choose the One Item with the highest number of additional starting watts. Take the equal numbers of running watts, add it to your Total Running Watts. You’ll need a generator that produces at least this many Starting Watts.

Example of conversion: 240 Volts X 5 Amps = 1200 Watts

In case, If only the running voltage is given on the nameplate for a device with an electric motor then the starting wattage can be calculate approximated to be three to five times the running wattage.

Now we calculate running and starting wattage requirements for the devices you are the desire to power can be calculated with the following steps:

  1. Write down all devices that consume power from the same time with the generator for some time.
  2. List the greater of the running or starting wattage next to the name of each device so that obtained from the devices in a manageable form.
  3. If only the running wattage for a device with an electric motor is mention then the starting wattage for the same can estimate to be at least 3 times the running wattage.

Advantages of picking the right sizing generator:

Now that you have an idea on how to choose the appropriate size of generator which suits your power requirements, here we listed just a few of the benefits obtained by going through that process of choosing the effective size of generators:

  1. No unexpected system failures.
  2. No shutdowns due to capacity overload.
  3. Increased longevity of the generator.
  4. Guaranteed performance.
  5. Smoother hassle-free maintenance.
  6. Increased system life span.
  7. Assured personal safety.
  8. Much smaller chance of asset damage.


These were the steps and concepts related to the sizing of generators. However. the article presented a summary of the common types of generators, characterized by fuel source and application.  In addition, steps to convert watts to amperes. Gives a bright light over the hard concepts of running watts and starting watts.

Furthermore, we mention every relative concept of generator sizing. So if you are having a difficult time with it or would like more specific suggestions and recommendations for your situation. Thus we hope now you will understand everything about generator and size  Please give us a thumbs up and share with your friends.

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