When the power goes out, the last thing you want is to realize your generator isn’t strong enough to run the essentials. Whether you're keeping food cold, running a home office, or just powering a few lights, choosing the right generator size is all about knowing your energy needs—and planning for the unexpected.
Generators are rated by running watts (the power needed to keep things going) and starting watts (the extra surge needed to turn things on). Appliances with motors—like fridges or air conditioners—often need a lot more power just to start up. For example, a typical refrigerator might only require 700 watts to run, but could spike to 2,200 watts at startup.
Simple Steps to Calculate Your Power Needs
Picking the right generator doesn’t have to be complicated. Here’s a quick, step-by-step method to get you there:
Start by listing every appliance or device you want to power during an outage—think refrigerator, microwave, sump pump, computer, modem, lights, and more.
Next, find the running watts and starting watts for each item. You can usually find these numbers on a label or in the user manual. Add up all the running watts to get a base total. Then, find the single appliance with the highest starting watts—this is your surge load.
Once you have both numbers, add them together, then multiply the result by 1.2 to give yourself a 20% safety margin. This buffer protects against sudden power spikes and ensures your generator isn't maxed out from the start.
An Example You Can Follow
Let’s say you want to run the following during a blackout:
Refrigerator: 700 running watts, 2,200 starting watts
Microwave: 1,000 watts
Computer: 800 watts
Monitor: 200 watts
Modem & Router: 100 watts
LED Lights: 300 watts
Add up the running watts:
700 + 1,000 + 800 + 200 + 100 + 300 = 3,100 watts
Then, identify the highest starting load:
2,200 watts from the fridge
Now, calculate your total power needs:
3,100 + 2,200 = 5,300 watts
Add a 20% buffer:
5,300 × 1.2 = 6,360 watts
In this scenario, a generator rated at 6,500 watts (or 6.5 kW) would be the smart choice.
What Common Appliances Actually Use
Here’s a quick look at how much power everyday items typically consume:
Appliance Running Watts Starting Watts
Refrigerator/Freezer 700 2,200
Microwave (1,000W) 1,000 1,000
Coffee Maker 1,000 1,000
Electric Stove Burner 2,100 2,100
Window A/C (10,000 BTU)1,200 3,600
Sump Pump (1/3 HP) 800 1,300
Electric Water Heater 4,500 4,500
Knowing these numbers helps you make smarter choices about what to run and when.
Tools to Make It Even Easier
Don’t feel like crunching the numbers yourself? Several online tools can help you estimate your needs:
Home Depot’s generator sizing guide lets you select appliances and get a wattage estimate tailored to your home. Sage Calculator offers a detailed breakdown with common appliance loads built-in, while StandbyAdvisor gives you a clear idea of what you’d need for a whole-home backup setup.
These calculators can help you avoid guesswork and make your decision easier.
Don’t Forget These Generator Features
While wattage is crucial, other features can also affect how well a generator suits your needs.
Fuel type matters—generators typically run on gas, propane, diesel, or natural gas, each with different storage and availability pros and cons. You’ll also want to think about portability. A small unit might work fine for basic needs, but a permanent standby generator is better for full-home coverage.
Noise levels are another consideration, especially in tight neighborhoods. Look for models that advertise quiet operation. Run time also matters. Longer run time per tank means less stress during extended outages. And don’t overlook maintenance—some models are lower-maintenance than others, but all need occasional checkups to stay reliable.
Stay Powered When It Matters Most
Selecting the right generator isn't just about numbers—it's about peace of mind. Knowing that your essentials will stay on when the power grid goes down can make a big difference in comfort, safety, and convenience. By understanding your true power needs and planning for a little extra capacity, you can choose a generator that won’t let you down when it counts.
