Generator Wattage Calculator

Generator wattage calculators can help you determine the right generator size to meet your electrical power needs. They are also an excellent way to compare different models side by side.

To make this process easier, use our wattage reference chart or refer to the owner’s manual of each device you wish to power. Typically, motor driven devices require more starting watts than non-motor devices.

Running Watts

Running watts (also called rated watts) are the watts needed for an appliance to stay on and run continuously. These watts are usually two to three times more than the starting watts.

A portable generator wattage calculator can help you figure out how much power you need to power your appliances and tools. This includes the wattage required by your sump pump, water heater, refrigerator, and furnace.

Start by looking at the wattage label or owner’s manual for your devices and appliances. Some are labeled in Volts-Amps while others are labeled in watts or kilowatts.

Next, look at how many watts are required for the highest power demand on your appliances and tools. For example, an electric water heater typically requires around 4,000 watts of electricity.

Then multiply these numbers by the number of items you have to power and add them up. This total will give you the running watts requirement for the device or appliance, including any extra watts required for the motor.

Starting Watts

Starting watts are the extra watts needed for two or three seconds to start motor-driven appliances. They are also called surge watts.

Most portable generators come with two wattage specifications: running watts and starting watts. Both are important to understand before buying a generator.

If you have a large family or work in an area that experiences frequent power outages, a high-wattage generator is essential to powering everything at once. To figure out how much wattage you need, calculate the running and starting watts for all the appliances that you want to use with your generator.

Devices that fall under resistive or capacitive load categories won’t require additional starting watts, so you can easily calculate their running watts by multiplying amps by volts. On the other hand, devices that fall under the inductive load category will need a higher starting watt than their running watts.

Surge Watts

Generator wattage calculators are an invaluable resource for determining the power required to operate appliances or tools. They also help you compare generators based on a variety of criteria and make sure that you purchase the right size generator for your specific needs.

When calculating generator wattage, there are two different elements to consider: Running watts and starting watts. Both are important to understand, but the distinction between them makes a big difference.

Running watts are the continuous watts that are needed to keep an appliance or device running steadily once it starts up. They can be higher than starting watts, especially when devices and appliances have an electric motor or compressor.


Amps is a unit of electrical power. It is equal to the number of electrons flowing through a wire per second.

When calculating watts, the voltage of a device is multiplied by the amperage to get a total wattage requirement. This is the amount of power that the device will consume from a generator.

Many appliances and tools will have a watt rating on their label or owner’s manual. They will also have a running and starting wattage for operation.

Several items like microwaves and combination heat pump/air-conditioners will require more power to start than they use during normal operation.

The watts needed by all of your appliances and tools are very important to determine what size portable generator you should buy. Having this information can save you money and hassle in the long run.