What size generator do I need for my house?
Picking the right generator size is about matching your backup power to what you actually need to run during an outage, without overspending on a huge unit you never fully use.
This guide walks through a simple way to think about generator sizing for different home sizes and backup goals. If you want quick estimates on runtime, rough size, and fuel cost, you can also use the calculators on the GeneratorCalc home page.
What size generator do I need for my house?
A simple way to estimate the generator size you might need for different home sizes and how much of your house you want to power.
Choosing the right generator size can feel confusing. You don’t need an engineering degree to get a useful answer, but you also don’t want to undersize your generator and end up tripping breakers every time a big appliance starts.
The good news: you can get a reasonable estimate by thinking about your home size, what you actually want to keep running, and whether you plan to run central air conditioning.
Start with how much of your house you want to power
Before you pick a generator, decide what your goal is during an outage:
- Essentials only: fridge or freezer, some lights, phone and laptop charging, internet, a TV, maybe a small window unit or space heater if needed.
- Most of the house: the same essentials plus more lights, more rooms, and a few bigger appliances such as a microwave, well pump, or electric range (not all at once).
- Nearly whole-home: many circuits on your panel, possibly including central air, electric dryers, or larger kitchen loads. This usually means a larger standby unit and professional installation.
The rough generator size planner near the top of this page is based on the first two scenarios: essentials only, or most of the house (without trying to power literally everything at once).
Rough generator sizes by home square footage
The table below shows very general ranges that many households fall into when they’re trying to power essentials or most of the home. These are approximate planning numbers, not strict rules.
| Home size (approx.) | Essentials only (typical range) | Most of the house (typical range) |
|---|---|---|
| Up to ~1,000 sq ft | 3–4 kW | 4.5–6 kW |
| ~1,000–2,000 sq ft | 4–5.5 kW | 6–8 kW |
| ~2,000–3,000 sq ft | 5.5–6.5 kW | 8–10 kW |
| Over ~3,000 sq ft | 6.5–7+ kW | 10–12+ kW |
If you want something more tailored than a table, you can use the rough generator size planner at the top of this page. Enter your approximate square footage, choose whether you want to cover essentials or most of the house, and decide if you’re planning to run central air.
Central air vs. no central air
Central air conditioning is one of the largest loads in a typical home. Running central A/C on a portable generator is not always practical, and often requires:
- A larger generator to handle the compressor starting surge
- Proper transfer equipment and wiring
- Input from an electrician to stay within code
Many people choose to size their generator for essentials and most of the home without central air, and then use fans, window A/C units, or portable units for cooling in specific rooms. Others choose a larger standby system that’s designed to handle central air and other heavy loads.
Why “a little bigger” is usually better than “barely enough”
A generator that’s right on the edge of what you need may work on paper, but in real life:
- Starting surges from fridges, pumps, and A/C units can cause voltage dips or breaker trips.
- You may feel like you’re constantly managing which circuits are on or off.
- Any future additions (new appliances, more devices) eat up your margin.
That’s why the size planner on this page shows a minimum size, a more comfortable size, and a more “future-proof” size. Planning for a bit of headroom usually makes outages less stressful.
Using the size planner on this page
The rough generator size planner further up the page is designed to make this decision easier. It asks for:
- Your approximate home size in square feet
- Whether you want to power essentials only or most of the house
- Whether you plan to run central air on the generator
Based on those, it estimates your approximate running watts, then gives three generator size suggestions:
- Minimum size: workable if you actively manage loads
- More comfortable size: better margin for starting surges
- More future-proof size: extra room for additional circuits or tools
These ranges are not a substitute for a detailed load calculation, but they are useful for comparing generator models and deciding whether you’re looking at something too small, reasonable, or comfortably sized for your goals.
When to involve a professional
If you plan to:
- Connect a generator directly to your home’s electrical panel
- Install a transfer switch or interlock kit
- Power central air or other large 240V loads
it’s wise to talk with a licensed electrician. They can perform a proper load calculation for your home, make sure your setup is code-compliant, and help you choose a generator that’s sized appropriately for how you actually want to live during an outage.
Bottom line
For many homes, a generator in the 3–7 kW range can cover essentials, and something in the 6–12 kW range can cover most of the house, depending on square footage and how many large appliances you want to run. If you’re not sure where to start, use the rough generator size planner on this page with your real-world numbers and use the suggested ranges as a starting point for your research.