What size generator do you actually need?
Select the essentials you want to keep running. We’ll estimate a practical backup-power range with headroom.
Motors and compressors can draw extra power when they start.
Choose what must stay powered
Your recommended product
Calculate above to see a matched option.
How to size a generator for a home outage
Generator sizing starts with the equipment you actually need during an outage—not the square footage of the house alone. Add the running watts of loads that may operate at the same time, then allow for the largest motor or compressor start-up demand and reasonable headroom. Always verify the nameplate ratings on your own appliances before purchasing or connecting equipment.
Typical appliance wattage planning ranges
| Appliance | Planning running watts | Possible start-up demand |
|---|---|---|
| Refrigerator | ~180 W | Up to ~1,200 W |
| Sump pump | ~800 W | Up to ~2,200 W |
| Well pump | ~1,000 W | Up to ~3,000 W |
| Window AC | ~1,000 W | Up to ~2,200 W |
| Small central AC | ~3,000 W | Up to ~6,500 W |
| Gas furnace blower | ~600 W | Up to ~1,400 W |
| Microwave | ~1,200 W | ~1,200 W |
| Wi-Fi + modem | ~40 W | ~40 W |
These are planning estimates used by this calculator, not universal appliance ratings. Actual equipment can vary materially by model, age and operating condition.
Running watts vs. starting watts
Running watts are the power an appliance uses while operating. Starting watts (surge watts) are the brief higher demand that some motors and compressors can require when they switch on. A generator can appear large enough based on running load and still struggle when a pump, refrigerator or air conditioner starts.
Common outage scenarios
Refrigerator + internet + basic lights
This is a relatively light emergency load, but the refrigerator compressor still creates a start-up consideration. Enter the exact devices you intend to run rather than selecting a generator from a generic “home size” label.
Refrigerator + sump pump + lights
A sump pump can materially change the required surge capacity. This is why homes with basements or drainage systems should size around the pump rather than treating it as an afterthought.
Adding air conditioning
Air conditioning can move a backup-power plan into a very different generator class. Central systems in particular require careful review of actual electrical specifications and the intended transfer setup.
Frequently asked questions
How many watts do I need to run a refrigerator during an outage?
The answer depends on the refrigerator. The calculator uses 180 running watts and up to 1,200 starting watts as a planning assumption, but you should use the rating information for your own unit before buying a generator.
What size generator do I need for a 2,000 sq ft house?
Square footage alone cannot determine generator size. A 2,000-square-foot home running only a refrigerator, lights and internet has very different requirements from the same home running a well pump, central AC and electric cooking. Size the generator from the loads you intend to power.
Should I add extra generator capacity?
Some headroom can help accommodate start-up loads and modest future needs, but oversizing also affects purchase price, fuel use and portability. This calculator lets you compare 20%, 30% and 40% planning headroom.
Can I connect a portable generator directly to my house?
Whole-home connections and transfer equipment involve serious electrical and carbon-monoxide safety considerations. Follow manufacturer instructions and applicable local requirements, and use a qualified electrician for permanent or transfer-switch installations.