Sizing a Generator for a Small House or Apartment

Most folks I meet think bigger is always safer. They call me up ready to buy a 12,000-watt beast to keep a one-bedroom apartment lit, and I have to talk them down. A generator that’s too large burns extra fuel, costs more up front, and half the time never runs at more than a third of its capacity. That’s a lot of money idling in the driveway.

The truth is, a small house or apartment usually gets by on far less than people expect. On a job last winter, a couple in a 900-square-foot ranch stayed warm, fed, and connected all through a three-day outage on a portable unit that cost them under $700. The trick wasn’t horsepower. It was knowing what actually needed to run.

So let’s figure out what you really need, in plain numbers, without the sales pressure.

Start with what you actually need to keep on

Before you shop for a generator size for a small house, make a short list. Not everything you own, just the things that make an outage bearable. For most people that’s a refrigerator, a few lights, a way to charge phones, and something to move air or make heat.

A mistake I see all the time is people listing their whole kitchen. You are not running the oven, the dishwasher, and the microwave at the same moment on backup power. You’re keeping food cold and boiling water. Be honest about the difference between “nice to have” and “need right now.”

If you want a fuller picture of household draw before you decide, this breakdown of how many watts a house actually uses is worth a read. It’ll ground your expectations in real figures instead of nameplate maximums.

Running watts versus starting watts

Here’s the part that trips up almost every beginner. Every appliance has two numbers: the running watts it sips once it’s going, and the starting watts it gulps for a split second when the motor first spins up.

A refrigerator might run at 150 watts but spike to 800 or more the instant the compressor kicks on. A window air conditioner is even worse, sometimes tripling its running number at startup. Your generator has to cover that spike, or it’ll stall right when you need it.

A quick way to estimate

Add up the running watts of everything you’ll use at once. Then take the single appliance with the biggest starting surge and add that surge on top. That total is roughly the peak your generator has to handle.

It sounds fussy, but it takes about five minutes with a notepad. And it’s the difference between a unit that hums along and one that keeps kicking off under load.

Real numbers for a small home

Let me show you what this looks like for an actual apartment. Wattage varies by model, so check the label on your own gear, but these figures are close to what I measure in the field.

Run the fridge, lights, chargers, router, and a window AC together and you’re around 1,090 running watts. Add the AC’s 2,200-watt surge and your peak lands near 2,600 watts. A 3,000-watt inverter generator handles that with room to spare.

Want to swap the microwave in while the AC runs? Now you’re pushing 3,600 peak, and a 3,500 to 4,000-watt unit makes more sense. For side-by-side model comparisons, the appliance wattage chart for generator sizing lays out dozens of common items.

Matching a generator size to your list

Once you have your peak number, sizing gets simple. Take that peak and add about 20% as a cushion. Generators shouldn’t run flat out for hours; a little headroom keeps them cooler and lasts longer.

Here’s how the common tiers shake out for small spaces.

• 2,000–2,200 watts: a studio or tiny apartment. Fridge, lights, chargers, no AC or heat.
• 3,000–3,500 watts: a one-bedroom. Fridge, lights, electronics, plus a window AC or small heater.
• 4,000–5,000 watts: a small two-bedroom house. All the above, plus a microwave or a well pump.
• 5,000–7,000 watts: the top end for a small home, if you want a couple of things running at once without thinking about it.

If your place is creeping toward 2,000 square feet or has electric heat, you’ve outgrown this bracket. Step over to the guidance on sizing a generator for a larger home instead, since electric furnaces and multiple AC units change the math completely.

Portable, inverter, or standby

For most small homes, a portable inverter generator is the sweet spot. It’s affordable, quiet, fuel-efficient, and you can wheel it out only when you need it. A good 3,500-watt inverter runs $600 to $1,000.

Standby units that wire into your electrical panel and start automatically are wonderful, but they’re overkill and often impractical for an apartment or a rental. If you own a small house and want that hands-off convenience, the rundown on whole-house standby generators covers what’s involved.

One thing worth planning early: if you ever want to power hardwired circuits instead of running extension cords, you’ll need a proper transfer switch installed by a licensed electrician. The overview of how transfer switches work explains why you can’t just backfeed through a dryer outlet. Please don’t. I’ve seen the aftermath.

Your next move

Grab a pen, walk your home, and write down every appliance you’d truly miss during an outage. Note the running and starting watts off each label, total them up, and add 20%. That number is your target, and it’s almost certainly smaller than what a salesperson will steer you toward.

If you want to double-check your math against a full walkthrough, the step-by-step guide on how to size a generator for your home takes it from list to purchase. For general storm and outage prep, the federal resources at Ready.gov’s power outage page are a solid reference. Buy for what you use, keep it maintained, and a modest generator will carry you through more outages than you’d guess.