What Size Generator Do I Need? Figuring Out Your Emergency Power Needs

What Size Generator Do I Need?

What Size Generator Should You Buy?

One of the first things to go during many disasters is the electricity. The obvious way to fix this problem is to buy a generator to power your essentials. When getting ready to buy a generator, one of the most common questions is what size generator do I need?

It sounds like an easy question but there are a lot of factors to consider. What does rated watts mean? What does surge watts mean? The power requirements for my device is listed in amps, how do I figure out if the generator can run it? These are questions that people tend to run into when they first look into a generator. It can all be overwhelming initially if you’re starting from scratch.

This article will answer all of these questions and more.

What Size Generator Do I Need?

What are Running and Surge Watts?

Understanding how generators are rated is the starting point for determining how much wattage you need in a generator. It may seem confusing, but it’s actually really easy.

Simply put, running (or rated) watts are the maximum number of watts that a generator can continuously output without damaging it. Running wattage is the consistent level of power that a device requires to run. Devices like hot plates and light bulbs will typically only have one wattage rating. This is their required running watts.

Surge (or starting) watts are the maximum amount of watts that a generator can output for a limited time. This allows the generator to ramp up its power output for a limited time to meet the demands of equipment and appliances that need more wattage to get started. These are almost always items with electric motors like refrigerators, washers, and driers.

Manufacturers almost always display the surge wattage as the wattage of the generator. Take this WEN 56200i Super Quiet 2000-Watt for example. It’s labeled as a 2000 watt generator, but that is its surge power level. The running wattage of this generator is 1600 watts. Other displayed ratings like max power, etc are all referring to the surge watts of the generator.

It’s not a big deal if you know what you’re looking for. Just be sure you read the label carefully and you’ll be good to go.

What Size Generator Do I Need If the Power Goes Out?

How Much Power Do My Devices Need?

The answer to this question will decide what size generator you need. First, you need to determine what you want to run off of the generator. Are you going to try to power your entire house or do you just want to keep your food in the refrigerator from spoiling until the power gets turned back on?

The table below will give you a rough idea of how much power you need to power certain devices. Keep in mind that these are just rough guidelines and you should get the exact power requirements from the labels on the equipment you plan to run on the generator.

Kitchen Devices Running (Rated) Wattage Surge (Starting) Wattage
Refrigerator or Freezer 700 1500
Microwave 1000
Coffee Maker 1750
Dishwasher 700 1400
Electric Oven 2100
Hotplate 1300
Household Utilities Running (Rated) Wattage Surge (Starting) Wattage
Furnace Fan 300-875 500-2350
Well Pump 1000 2000
Central Air Conditioner 3800 4950
Electric Water Heater 4000
Window Air Conditioner 1200 2200
Box Fan 200
Washing Machine 1150 2300
Household Electronics Running (Rated) Wattage Surge (Starting) Wattage
Television 140-300
Desktop Computer 600-800
Laptop 65
Charging Mobile Devices 10-12
Electric Grill 1650
Space Heater 1800
Radio/CD/DVD Player 50-200
Power Tools Running (Rated) Wattage Surge (Starting) Wattage
Circular Saw 1400 2300
Table Saw 1800 4500
1 HP Air Compressor 1600 4500
Battery Charger 2400-7800
Bench Grinder 1400 2500
Drill 600 900
Electric Welder 5000

How Do I Figure Out Power Requirements for a Device if it’s Listed in Amps?

Figuring out the power requirements for a device if it’s listed in amps is easy.

Wattage is determined by multiplying volts x amps.

Most generators output 120 volts.

So if a device needs 10 amps to power it, you would simply multiply 120 volts x 10 amps to figure out that you need 1200 watts of power to run it.

How Do We Determine How Much Power Our Generator Has to be Able to Output?

Now that we understand the basics of how generators are rated and what the rating means, let’s look at how we figure out the exact size of generator we need.

Keep in mind this will be the least powerful generator that will run your appliances or devices. The more power that your generator can output, the more items you’ll be able to power.

In the first example, we’ll say that we just want to power the minimum number of things needed during a power outage.

Scenario #1 Running (Rated) Wattage Surge (Starting) Wattage
Space Heater 1800 1800
Laptop 65 65
Charge Phones/Devices 12 12
Hot Plate 1300 1300
Total 3,177 3,177

In this scenario, we’ve determined that we want to be able to charge our phones, run a space heater, charge our laptop and cook on a hotplate. So if we wanted to run everything at once, we’d need 3177 running watts. Something like a DuroStar DS4000S would be sufficient. If we decided not to ever run the heater and hot plate together, we could even drop down to a 2000 watt generator.

In the second example, we’ll say we’re looking for a generator to provide back up power for our entire house.

Scenario #2 Running (Rated) Wattage Surge (Starting) Wattage
Central Air Conditioning 3800 4950
Electric Water Heater 4000 4000
Refrigerator or Freezer 700 1500
Microwave 1000 1000
Dishwasher 700 1400
Electric Oven 2100 2100
Well Pump 1000 2000
Furnace Fan 600 1500
Electric Water Heater 4000 4000
Television 300 300
Laptop 65 65
Total 18,265 22,815

In this scenario, we’re looking for something to power our entire home during a power outage. Obviously, this is going to take a much larger and expensive generator.

What Size Generator Do I Need to Power My House after a power outage?

This example would need something like a Generac 7043 Guardian Series 22kW/19.5kW standby generator. Having a standby generator for your home is great because it’s already wired in and can seamlessly switch on when the power goes out. 


Buying a generator for an emergency is a great option for anyone who is preparedness minded. Being able to generate your own power can add a lot of versatility to your preparedness plans.

Deciding to buy a whole house standby generator is an expensive option that most people probably won’t decide on. A portable generator, on the other hand, can be a great choice for short-term power outages.

Be sure to check out our other gear related articles here!

Additional Reading: The Best Bug Out Bag List – What You Need and Why You Need It!

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