Generator Sizing Calculator

Generator Sizing Calculator

Generator Buying Tips


Amazon has created an excellent manual to help you get to the right generator for your needs.  Make sure you see it once before you make a final selection of your favorite Generator.

generator buying guide

And a Transfer Switch is a safety feature which should definitely be a top priority, unless your Generator is used occasionally or not connected to your Main Panel.

Generator Transfer Switch

Whether you looking for a : standby generator or a portable generator or  inverter Generators or a quiet generator or a quiet portable generator or a camping generator, or a PTO Generator (Power Take Off), you will find a great selection of the best generators on this website. Before you start your generator adventures there are a few things you must know.

Things to Know Before You Buy

There are a two basic numbers you will need to determine before you buy a generator : what would you like to power? and how many watts do you need?  Since you are reading this, you are already ahead in the game; you are getting informed and taking control by gathering information.

Spending a little time with a calculator in hand on this page will lead you to your perfect generator. This buying guide will make your buying process relatively pain free. So ready :

What Size of Generator do I need

STEP 1.    What would you like to power ?

Are you you planning a tailgate party or is it for camping ? Do you want to use it as an emergency backup. Depending on your requirements, decide on a list of appliances which your generator will have to power. Use this table below to select the appliances you want to power. Then move to SETP 2 which is below the table.

ApplianceRunning WattsStarting WattsApplianceRunning WattsStarting Watts
Box Fan 20″2000Laptop2000
String Lights20042″ Plasma TV2400
RV AC (13500btu)16002300Inflator Pump50150
Tablet500Phone Charger150
EssentialsRunning WattsStarting WattsEssentialsRunning WattsStarting Watts
Sump Pump 1/3hp8001300Sump Pump 1/2hp11002200
Well Pump 1/3hp10002100Sump Pump 1/2hp11002200
Light 60W600Electric Water Heater40000
Space Heater18000Furnace Fan 1/2hp8002400
Furnace Fan 1/3hp7001400Window AC 10,000btu12003600
Central AC 10,000btu15003000Central AC 24,000btu38004950
Central AC 40,000btu60006700Heat Pump45004700
Iron12000Washing M/C11202250
Dryer Electric54001350Dryer Gas7001800
Microwave 625w6250Microwave 1000w10002250
Coffee M/c10000Elec Oven34000
Toaster8500Elec Can Opener1700
XBox1500DVD Player3500
42″ Plasma TV240032″ LED TV500
Desktop Computer8000Hair Dryer12500
Security System5000Laser Printer5001200
Circular Saw12002400Disc Sander 9″12001200
Halogen Light3000Paint Sprayer3601080
Electric Drill 1/4″300300Cordless Drill Charger70150
Elec Lawn Mower14004300Elec Pressure Washer12003600
Elec Chainsaw12002400Elec String Trimmer6001500
Elec Weed Trimmer500500   

STEP 2.    How many watts do you need ?

After Step 1, you should have a list of appliances devices which your generator must power. Here is an example of what your list might look like :

ApplianceRunning WattsStarting Watts
Box Fan 20″2000
String Lights200
42″ Plasma TV2400
RV AC (13500btu)16002300
Inflator Pump50150
Phone Charger150
ADD Running Watts of all your appliances  200 + 200 +20  + 240 + 1600+ 50 + 50 + 15 = 2375 watts
Choose the appliance with the largest Starting Watts, in this case it is the RV AC with 2300 starting watts.  Add that to the Running Watts 2375 +2300  =  4675 watts
Your GENERATOR needs to be produce at least 4675 watts  – so a 5000 watt generator is your best choice.

The Generator  Sizing Calculator says you need a 4675 watts generator. Your best choice would be the next largest size which would be 5000 watts or 5KW generator.

Budget for Generator

Now that you have established your generator size, you need to make sure your budget will be able to buy that size of generator. Sometimes you might have to compromise and buy a lower power portable generator instead of a standby generator that you might have established to be your required generator size.  A Transfer switch is and additional item that you will need to safely power the circuits in your home. Would you need the services of an electrician to install your generator or are you a proficient DIY er.

Included Items with Generator

What about the items in the generator package. Is the warranty and maintenance package upto snuff ? You need to determine if the generator comes with power cord, oil, wheels, a cover, a funnel etc. And the transfer switch is very important. Does it come included?  How much for installation ?

Different Generator Types

The two main Generators types are the : Standby generator and the Portable generator . There is another generator type know as  Inverter Generators which are quieter and are gaining popularity. If you are environmentally conscious you might like to go for a Solar generator. There is a whole section on this website devoted to Solar Generators.

Standby generatorStandby Generators:  The largest class of geneators starting at about 7,000 watts and going upto 20,000 watts or more. These standby generators with capacities from  7KW to 20 KW typically offer 24 hour home blackout protection.

They are professionally installed with Transfer switches and automatically start during a power outage and are able to provide your home with enough power to either meet all your needs or your critical needs depending on the size of generator.

The larger standby generators are called whole home generators or Home Standby Generators and draw fuel from existing natural gas or propane supply lines. They are usually installed on concrete pads and are enclosed with generator covers.

They are permanent installs and cannot be moved around They cost between $3000 to $ 40,000.  Installation usually requires a town permit.

Portable generator

Smaller standby generators can cost between $3,000-$15,000 and are usually standalone units that don’t require professional installation.

You should check their dimensions and power output carefully before selecting a unit.  The smaller standby generators are best for job sites as they offer mobility are  powerful enough to run a variety of tools.

Make sure you use the Generator Sizing calculator to cover your running and starting watts needs. Construction Professionals may also like to check for features like auto-idle technology, roll cage frames and flat-free wheels.

The smallest generators are the Portable Generators that are priced between $100-$3,000 and range in power from 1000 to 10,000 watts. They are best used for leisure activities or for a few hours of backup during an outage.

Choosing a portable generator boils down to making choices about their wattage, how long they are able to run and finally their size and portability.

Depending on your needs you  might want to make sure they support outputs such as the 120-Volt RV Outlet, 12 V DC and USB in addition to standard AC outputs.

The final class of generators are the Inverter generators which are seen more in use among the camping boating and RV communities.  Inverter-GeneratorInverter-Generators with their quiet clean operations and relatively small sizes make them a good choice for your next tailgating party.

Inverter generators can cost anywhere between $150-$6,000. Power ratings of inverter generators stretch from 500-3,000 watts. They make a good choice for their clean power, efficiency and size.

A great benefit of the Inverter Generators is their low Total Harmonic Distortion (THD) making them super safe for all electronics. If their smaller wattage deters you, you might consider buying two and connecting  them with a parallel kit.

Generator Safety

Make sure you read the owner’s manual and instructions and carefully follow all instructions and warnings in order to safely start and operate the generator.  Some standard operating rules are :

You must not connect your generator directly to your home’s electrical wiring, especially not to a regular outlet. This can ‘back feed’ onto the power lines and injure neighbors or utility workers.

Generator Transfer Switch
Generator Transfer Switch

Use a transfer switch.

Have proper grounding for your generator and follow all township guidelines and permits.

Never run a generator indoors

Don’t run in an enclosed area  such as garages.

Operate outdoors and away from windows, doors, vents and crawl spaces

Make sure there is adequate ventilation around the generator

Open doors and windows  with a running fan will not provide ventilation.

Generator should be on a flat surface and not be exposed to excessive moisture, dirt, dust or corrosive vapors

The fuel tank must not be overfilled. There must be room for fuel expansion. 

Only add fuel while the unit is cold and never while it is running or hot.

There is plenty more to see in the solar world. Check out these articles. Thank you for visiting

Generator Buying Guide – The End

Author: Michael Bennet

A Solar energy professional with ten years of marketing and installation experience. Avid and passionate about the adoption of solar and related technologies in all homes. Blogs about all things solar and sustainable at

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