How Many Watts Does Your Generator Need?

Understanding watts on a generator listing

When you look at a generator listing, you'll see two watt figures: starting watts and running watts. Starting watts, sometimes called surge watts, is the brief burst of power a generator can deliver when a motor first turns on. Running watts is the steady power it can supply while the motor runs. Most appliances with a motor, like a refrigerator, a sump pump, or a power tool, need more watts to start than to run.

The first watt figure in a listing title is often the starting watts, because that's the larger number. The running watts is usually listed in the product details or on the maker's page. When you compare generators, look for both figures so you know what the unit can handle for a sustained load and what it can handle for a quick start. For more on these terms, see generator running watts vs starting watts.

• Starting watts: the peak power needed for a few seconds when a motor starts.
• Running watts: the continuous power needed to keep the device operating.
• A generator's starting watts must cover the sum of running watts plus the largest starting surge.

How to calculate your load

Start by making a list of everything you want to power at the same time. For each item, find its running watts and starting watts. You can usually find these on the appliance's nameplate, in the owner's manual, or on the maker's website. If a device doesn't have a motor, like a light bulb or a TV, its starting watts are the same as its running watts.

Add up the running watts of all the items you'll run simultaneously. Then add the highest starting watts among those items. The total is the minimum starting watts your generator should provide. For example, if you want to run a refrigerator (running 600 watts, starting 1,200 watts), a sump pump (running 800 watts, starting 1,300 watts), and a few lights (running 300 watts), your total running watts would be 1,700 watts, and the highest starting surge is 1,300 watts, so you'd need a generator with at least 3,000 starting watts.

Common appliances and their wattage ranges

While exact wattage varies by model, here are typical ranges for common household items. These are general estimates; always check the specific device's nameplate for accurate figures.

For a home backup scenario, you might prioritize a refrigerator, a sump pump, a furnace fan, and a few lights. For camping or an RV, you'd focus on a small refrigerator, a microwave, and a coffee maker. For a job site, you'd consider power tools like a circular saw or a compressor. See generator for home backup sizing for more on home scenarios.

• Refrigerator: running 600-800 watts, starting 1,200-2,000 watts
• Sump pump: running 800-1,000 watts, starting 1,300-2,000 watts
• Microwave: running 1,000-1,500 watts, starting same as running
• Coffee maker: running 800-1,200 watts, starting same as running
• Circular saw: running 1,200-1,500 watts, starting 2,400-3,000 watts
• Air conditioner (window unit): running 1,200-1,500 watts, starting 2,400-3,000 watts

Matching your load to a generator size

Once you have your total starting watts, you can look for a generator in that range. This site groups generators by wattage, such as 3,000 to 5,000 watts and 5,001 to 9,000 watts. If your calculated need is around 3,000 starting watts, a generator in the 3,000 to 5,000 range would be a starting point. If you need more for a whole-house backup, you might consider a standby unit, which is installed by a professional.

Remember that running watts matter too. If your total running load is 1,700 watts, you need a generator that can sustain at least that much. The running watts figure on a listing tells you that. For a home backup, you'll want to run the essentials, not everything at once. For an RV, you'll need to manage your usage to stay within the generator's running capacity. Check best generator for RV for RV-specific advice.

What this site cannot tell you

This site compares generators based on stated details from listings, not measured output. The wattage figures on a listing are the manufacturer's stated numbers, and actual performance can vary. For precise sizing, especially for a home backup, consult a licensed electrician and the generator maker. They can help you calculate your exact load and choose a unit that meets your needs.

Also, this site does not provide advice on connecting a generator to your home's wiring. That requires a transfer switch or interlock, and only a licensed electrician should do that work. For portable use, always follow the maker's manual for safe operation, and never run a generator indoors. Read the carbon monoxide safety information from the CPSC and CDC. See best portable generators for portable options.

What to pick for your situation

Questions

What is the difference between starting watts and running watts?

Starting watts, or surge watts, is the brief burst of power a generator can deliver when a motor first turns on. Running watts is the steady power it can supply while the motor runs. Most motor-driven appliances need more watts to start than to run.

How do I find the wattage of my appliances?

Check the nameplate on the appliance, which lists voltage and amperage. Multiply volts by amps to get watts. For example, 120 volts times 5 amps equals 600 watts. The owner's manual or the maker's website also often lists wattage.

Can I run my whole house with a portable generator?

A portable generator can power selected circuits, but it cannot run everything at once. You'll need to prioritize essentials. For whole-house backup, a standby generator is designed for that purpose and is installed by a professional. See best whole house generators for options.

What happens if my generator's starting watts are too low?

If the starting watts are too low, the generator may not be able to start a motor-driven appliance, causing the appliance to not run or the generator to overload. It's important to size your generator to cover the highest starting surge.

Do I need a generator with more watts if I use an air conditioner?

Air conditioners have a high starting surge, often two to three times their running watts. You'll need a generator that can handle that surge. Check the AC's nameplate for the locked rotor amps or starting watts. See generator for RV air conditioner for RV AC specifics.

Is it better to have a generator with more watts than I need?

Having extra capacity gives you flexibility to add more appliances later, but it also means a larger, heavier, and more expensive unit. It's best to size based on your actual needs, with a small margin for unexpected loads.