The choices might be limited if you’re looking for a generator in the middle of an active hurricane season, like the one we’re experiencing now. But even if you’re in a hurry, you'll want to take time to match your power needs to the size of the generator you buy.

Can you get by for a few days with just the basics—keeping your food cold and your lights on—or do you want to power your central air conditioner or heating system? "The first thing you need to know when selecting a generator, is how much power will you need, says Dave Trezza who tests generators for Consumer Reports. "Are you planning to use everything in your home or just the basics like keeping your food cold, your lights on, and charging phone/laptops."

When it comes to choosing the right size generator, here's what the pros at Consumer Reports recommend.

What to Know About Types

Generators come in two types: portable and stationary, also called standby. Portables cost less to buy and install, but you’ll need to fuel it and maintain it. A portable also needs to be wheeled outdoors, started, and connected to what you want to power. A stationary model, by contrast, needs to be professionally installed outdoors, which adds time and expense, but it starts automatically when power cuts off, performs its own periodic maintenance checks, and alerts you when it needs to be serviced.

What to Know About Wattage

To determine generator size, the easiest way is to add up the wattages of everything you want to power in your home Keep in mind that some appliances, such as air conditioners, refrigerators, and sump pumps, require more wattage (called surge watts) when they’re cycling on. It can also be difficult to gauge how much power certain hard-wired appliances, such as your furnace, require. Our experts suggest consulting with an electrician, and selecting a model with a slightly higher rated wattage to accommodate your existing needs but also handle anything additional you might add later.

Storm Survival

Also, plan to spend a few hundred dollars to install a transfer switch, which allows easier connections for a portable generator. (Stationary generators often come with one.)
"Whenever using a portable generator use a transfer switch," says Trezza. "This is the safest and easiest way to transfer power into your home and it protects any utility workers who may be working on the line."

Our generator buying guide lists the various wattage ranges that portable and stationary generators will support.

Get Wise About Size

To figure out what generator size you need, check out Consumer Reports' cheat sheet, which matches the size to your needs.

Small portable: 3,000 to 4,000 watts
What it can power: The basics, including a:

  • Refrigerator (600 watts)
  • Microwave (1,500 watts)
  • Sump pump (600 watts)
  • Several lights (400 watts)
  • TV (200 watts)

Midsized portable and small stationary: 5,000 to 8,500 watts
What it can power: Same as small portables, plus a:

  • Portable heater (1,300 watts)
  • Computer (250 watts)
  • Heating system (500 watts)
  • Second pump (600 watts)
  • More lights (400 watts)

Large portable: 10,000 watts
What it can power: All of the above, plus a:

  • Small water heater (3,000 watts)
  • Central air conditioner (5,000 watts)
  • Electric range (5,000 watts)

Large stationary: 10,000 to 15,000 watts
What it can power: Same as large portable models, plus a:

  • Clothes washer (1,200 watts)
  • Electric dryer (5,000 watts)

If possible, try not to wait until a major storm is forecast to buy a generator. In addition to facing a more limited selection, you’ll cheat yourself out of the weeks you need to plan your purchase and get it installed before you can enjoy the protection of a generator that will serve you for storms to come.

Some Top Performers

Here are some recommended models from our generator Ratings of dozens of portable and stationary generators:

Kohler PRO7.5E, $1,400, a 6,300-watt portable that supplied plenty of power, and cleanly, with less noise than many competing models;
Generac RS7000E, $900, a 7,000-watt model that performed nearly as well;
Generac 6237, $2,250 (with transfer switch), a stationary generator that delivers 7,000 watts using natural gas and 8,000 using propane; and
Kohler 14RESAL, $3,700 (with transfer switch), a larger stationary generator that supplied 12,000 watts using natural gas—and 2,000 more with propane.