The practical 2025 guide to emergency generator sizing — what to prioritize, what to skip, and the exact generator size for short and extended outages in any home.
A power outage strips your home down to what actually matters. Before you reach for a generator spec sheet, you need to decide: what do I actually need to keep running? The answer to that question determines whether you need a $500 inverter or a $5,000 portable, and it changes the entire sizing calculation.
💡 Already know your must-have appliances? Use our free generator size calculator to check them off and get an instant wattage recommendation — no math required.
Not everything in your home is equally important during an outage. Before sizing a generator, categorize your loads into tiers:
Short outages don't require powering everything — just keeping the critical loads alive until power returns. Refrigerator (175W running / 1,200W starting), lights (100W), and chargers (150W) total about 425W running with a ~1,200W surge. A 2,000W inverter generator handles this cleanly and quietly.
Extend the load to include a sump pump (900W running / 2,000W starting), TV (125W), and microwave bursts (1,000W):
Running: 175 + 100 + 150 + 900 + 125 = 1,450W running.
Peak (sump pump starting): 1,450 + 2,000 = 3,450W peak.
A 3,500–5,000W generator covers this with comfortable margin. This is the most common real-world outage setup for storm season.
Add a window AC (1,100W running / 2,500W starting) or furnace fan (700W running / 1,200W starting) to Scenario B:
Running: 1,450 + 1,100 = 2,550W running.
Peak (AC starting, largest surge): 2,550 + 2,500 = 5,050W peak.
A 7,500W generator (9,375W surge) handles this with headroom for a well pump or second AC unit. This is the right size for hurricane and ice storm country.
Running central AC (3,500–5,000W running / 7,000–10,000W starting) on top of everything else pushes requirements past what most portable generators can safely supply. A 10,000–12,000W portable generator can handle central AC if everything else is modest. True whole-home coverage — including all 240V circuits — requires a standby generator in the 13–22 kW range. See our portable vs. standby guide for more.
| Household Type | Recommended Size | What It Powers |
|---|---|---|
| Apartment / small home, no pumps | 2,000 W | Fridge, lights, chargers, small TV |
| Typical home, no AC/pump | 3,500 W | Above + sump pump (1/3 HP) or window AC |
| 3-bedroom home, sump pump | 5,000 W | Above + window AC + well pump |
| 3-bedroom home, full summer outage | 7,500 W | Above + larger window AC + furnace fan |
| Large home, central AC | 10,000 W+ | Central AC + all essentials + some 240V loads |
| Whole-home automatic backup | 13–22 kW standby | Everything, automatic, unlimited runtime on gas |
Every year, people die from carbon monoxide poisoning while running generators during storms. Here are the non-negotiable safety rules:
Covers the essentials for most homes — fridge, lights, sump pump, and TV — at the lowest entry cost. Pair with an interlock kit for safe panel hookup.
→ Browse 5,000W Outage Backup Generators on Amazon
Handles everything a 3-bedroom home needs including a window AC and sump pump. Dual-fuel flexibility is essential for extended regional outages when gas supplies are disrupted.
→ Browse 7,500W Dual-Fuel Storm Generators on Amazon
Permanently installed, starts in 10 seconds, runs on natural gas or propane, powers most of the house automatically. The right choice for frequent-outage regions or households with medical equipment.
For essentials (refrigerator, lights, chargers, sump pump), most homes need 5,000–7,500W. If you add a window AC unit, 7,500W is recommended. For central AC or whole-home coverage, you're looking at 10,000W portable or a 13–22 kW standby generator. Use our free calculator to get the exact number for your specific appliance list.
When running only essentials (not everything at once), most homes draw 1,000–3,000 watts continuously during an outage. The generator needs to be larger than that because motor starting surges create brief peaks of 3,000–7,000 watts. Always size to peak demand, not average demand.
A basic 2,000W inverter generator for minimal backup costs $400–$700. A 5,000W generator for essential circuits costs $600–$1,200. A 7,500W dual-fuel generator costs $800–$1,800. Add $300–$800 for a transfer switch installation. A 14 kW standby generator with installation runs $8,000–$14,000. Most homeowners find the 5,000–7,500W portable setup at $1,000–$2,500 all-in to be the best value.
A 5,000–7,500W generator at 50–60% load typically runs 8–12 hours per tank of gasoline (4–6 gallon tanks are common). Dual-fuel models running on a 20 lb propane tank run 5–8 hours. With a large 100 lb propane tank, you can run for 30–50+ hours between fills. Standby generators on a natural gas line run indefinitely without refueling stops.
Avoid plugging in high-wattage resistive loads you don't need: electric dryers (5,400W), electric water heaters (4,000W), central electric heat (10,000W+), or electric ranges (8,000–10,000W). Also avoid daisy-chaining extension cords or using undersized cords — use 12 AWG for most loads and 10 AWG for motor loads over 1,500W.
Free tool — check off your appliances, get your size in 60 seconds.
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