Portable Generator Sizing and Wattage Calculator

Select the most necessary electrical appliances to understand your power requirements.


laptop chargerLaptop Charger
desktop computerDesktop Computer
lcd monitorLCD Monitor
laser printerLaser Printer
inkjet-printerInkjet Printer
mobile phone chargerMobile Phone Charger

Household Utility

surnace fanSurnace Fan
sump pumpSump Pump
Well PumpWell Pump
Room Air ConditionerRoom Air Conditioner
Central Air ConditionerCentral Air Conditioner
Box FanBox Fan
Ceiling FanCeiling Fan
Led BulbsLed Bulbs (x4)
Electric Water HeaterElectric Water Heater
Washing MachineWashing Machine
Clothes DryerClothes Dryer
Garage Door OpenerGarage Door Opener

Household Kitchen

Coffee MachineCoffee Machine
Electric skilletElectric skillet
Electric stoveElectric Stove


Electric WelderElectric Welder
Air CompressorAir Compressor
Circular SawCircular Saw
Electric DrillElectric Drill
Belt SanderBelt Sander
Running Watts:
Starting Watts:

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All calculations are approximate!

How to calculate your Generator’s Wattage and those of your Appliances

When you are planning to buy a power generator for your electrical appliances and/or tools, knowing the required watts, which is the electrical power, is very important. There is no need of buying the 10000 watt generator when your electrical need is lightweight. And at the same time, there is no need of buying a less powerful generator that will not power all your electrical appliances sufficiently, and efficiently.

The only way to make sure that you are buying the right generator is knowing both the generator’s electrical watt output, and the watts needed by your electrical appliances and tools. This information will help you in sizing your budget according to your electrical power needs.

Also, you should know that different electrical appliances need different watts of electrical power for operation, depending on such factors as what they’re used for, and their manufacturer’s designs. As such, not all your appliances will require the same amount of watts to operate. Some require more power surge than others. Therefore, you should take into considerations the minimum and the maximum electrical power output (watts) that all your electrical appliances need. Make sure that the portable generator that you are buying is capable of providing your appliances and tools with the electrical power that they need. This will set you ahead of schedule.

How Can You Determine the Power Needed by All your Electrical Appliances?

Basically, there are two ways that you could use to determine the amount of electrical power that your tools and appliances need. Most electrical appliances and motors quantify their power needs in amps, which is the unit for current. Finding the amps needed by your electrical appliance and/or tool is a simple task. This information is contained on a stamp on the bottom side of your appliance; the nameplate; and the data tag which are found on all electric motors. This is one way of finding the amount of electrical output that your appliances need.

The other method involves using a load tester to determine how big of a generator do i need. A Honda handheld load tester could help you determine all your appliances electrical needs. Just test them one by one and you will find the total power output that they would require. Please note that some appliances rate their electrical power needs in amps. The electricity generator will rate its electrical power output in watts. For you to know the right generator that will provide you with the power that your equipment need, you will have to convert amps into watts.

How Then, Can You Convert Amps into Watts?

In the electricity field, there’s Ohm’s law, which you could use to convert amps into watts, and vice versa. The Ohm’s law states that voltage is equal to the product of current and resistance. This means that you will multiply amps by resistance for you to get the voltage of a particular electrical appliance. The same law says that power (Watts) is equal to voltage multiplied by current.

Since most electrical appliances use 120 volts, you could just multiply this voltage by the amps of the device. You will get the watts that the electrical appliance in question needs, for it to run or operate efficiently. From the forgoing, watts equals the product of voltage and the current (amps). For example, if a bulb uses 120V and its current is 150mA, then its wattage becomes 18 watts. A milliamps (mA) is equal to 0.001 Amps. 18 W is the answer you get when you multiply 120V by 0.15 Amps (150mA). Amps is, then calculated by diving watts by the volts.

And for you to determine how much power you need from an electricity generator, you will add all the watts of your electrical appliances.

The Difference Between Starting Wattage vs. Running Wattage

The starting watts is the electrical power needed by your appliance to start running. The running wattage is the amount of power it needs to continue operating. Often, the starting watts is higher than the running watts, by up to 3 times. When buying a generator, you will have to consider each appliance’s starting and running watts, for an efficient electrical power supply.

There are two major types of loads (electrical appliances): The resistive loads; and the reactive loads. Resistive loads require the same starting and running watts. On the other hand, the reactive loads (appliances) require a higher starting watts than their running watts. Loads such as light bulb, and toaster are resistive loads. On the other hand, loads such as freezers, furnace fans, well pumps, air conditioner and power tools, just to mention a few, are referred to as reactive loads.

Reactive loads have electric motors and fans, which need additional electrical power thus a higher starting wattage. Freezers and furnace fans therefore, need a higher starting wattage to get your systems up and running. Therefore, don’t rush while buying a generator for your electrical loads/appliances. Take some time and research your generators.