What size generator do I need?
Pick what stays on when the power goes out. You get the watts, the right type and the models that fit.
Start from
What stays on
2,160 W running- Refrigeratorsurge
- Sump pump, 1/2 HPsurge
- LED bulb
- Internet router and modem
- Phone or laptop charger
- TV, 32 to 55 in
How long is the outage
Advanced
| Appliance | Running W | Start-up W | Use per day | Wh in 1 day |
|---|---|---|---|---|
| Refrigerator | 400 | +1,200 | all day | 1,400 |
| Sump pump, 1/2 HP | 1,050 | +2,150 | 2 h | 2,100 |
| LED bulb × 6 | 90 | – | 6 h | 540 |
| Internet router and modem | 20 | – | 24 h | 480 |
| Phone or laptop charger × 2 | 200 | – | 3 h | 600 |
| TV, 32 to 55 in | 400 | – | 4 h | 1,600 |
| Total | 2,160 | +2,150 | 6,720 |
- Starting
2,160 running + 2,150 largest start-up = 4,310 W - Running
2,160 × 1.20 headroom = 2,592 W, rounded up to 2,600 W - Battery
6,720 Wh ÷ 85% inverter × 1.20 headroom = 9,487 Wh
Headroom 20% · inverter efficiency 85% · fuel gas. Change these under Advanced.
You need about
4,400W starting
2,600 W running
Running load is 83% of that size
Best fit
Portable generator
A battery would need about 9,490 Wh. A generator covers this on fuel you can store.
- Portable generator
- 2,600 W run · 4,400 W start
- Power station
- 9,490 Wh · 2,160 W out
- Standby generator
- 10 kW
Sump pump, 1/2 HP sets the starting size. Its start-up surge adds 2,150 W for a moment.
See 4 models that fitRun a generator outdoors only, 20 ft or more from windows, doors and vents. Never in a garage. CDC
The short answer
Add the running watts of everything you'll use at once. Add the biggest single start-up surge. Then add 20% headroom. For a fridge, a sump pump, lights, Wi-Fi and a TV, that comes to 4,400 W starting and 2,600 W running. Champion puts the essentials of a typical 2,000 sq ft home at 5,000 to 7,500 W.
Models that meet your numbers
Checked against each manufacturer's published specs on October 11, 2026. Links go to the manufacturer. If we add affiliate links, we may earn a commission. That never changes which models pass. Disclosure
| Model | Rating | Your numbers | Runtime or fuel | List price | Link |
|---|---|---|---|---|---|
| Champion4500W Dual Fuel Inverter (201531)Inverter generator | 3,250 W run · 4,500 W start | Running StartingMeets your needs | Gas / propane · CO shutoff | — | Specs |
| Champion7500W Dual Fuel, electric start (201281)Portable generator | 7,500 W run · 9,375 W start | Running StartingMeets your needs | Gas / propane · CO shutoff | — | Specs |
| GeneracGP8000E COsensePortable generator | 8,000 W run · 10,000 W start | Running StartingMeets your needs | Gas · CO shutoff | $1,179$147/kW | Specs |
| WestinghouseWGen9500DFPortable generator | 9,500 W run · 12,500 W start | Running StartingMeets your needs | Gas / propane | — | Specs |
How we calculate
Add up running watts
Each appliance uses the top of the range in Champion's published wattage chart, so the answer errs on the safe side. Edit any number to match your label.
running = Σ watts × quantityAdd the biggest start-up surge
Motors in fridges, pumps and air conditioners need a short burst to start. Only one usually starts at a time, so we add the single largest surge. That is Champion's method.
starting = running + largest surgeLeave headroom
We add 20% to the running total so the generator isn't working at its limit, then round up to the next 100 W.
size = running × 1.2
Full method, battery maths and limits: How we calculate.
Wattage of common appliances
| Appliance | Running W | Extra to start |
|---|---|---|
| Refrigerator | 150–400 | 800–1,200 |
| Freezer, upright | 100–500 | 500–1,000 |
| Sump pump, 1/2 HP | 800–1,050 | 1,300–2,150 |
| Well pump, 1/2 HP | 750–1,000 | 1,500–2,000 |
| Furnace fan, 1/2 HP | 300–800 | 800–1,600 |
| Window AC, 10,000 BTU | 900–1,200 | 1,800–2,400 |
| Central AC, 3 ton | 3,000–3,500 | 5,000–6,000 |
| Microwave | 600–1,200 | – |
| Washing machine | 500–1,000 | 1,000–2,300 |
| Space heater | 750–1,500 | – |
| TV, 32 to 55 in | 80–400 | – |
| CPAP, no humidifier | 30–60 | – |
Ranges from Champion Power Equipment. All 31 appliances
Worked examples
One day on the essentials
Fridge, sump pump, six lights, Wi-Fi, two chargers and a TV. 1 day.
4,400 W start · 2,600 W runThree days on a well
Well pump, fridge, freezer, lights, microwave and Wi-Fi. 3 days.
5,300 W start · 3,900 W runA CPAP through the night
CPAP with a heated humidifier, a phone charger and two lights. 12 h.
2,040 Wh · Power station
Generator, power station or standby
| Portable generator | Power station | Standby generator | |
|---|---|---|---|
| Best for | Essentials for days | Small loads, medical devices, apartments | The whole house, including central air |
| Use indoors | Never | Yes | Installed outside |
| Noise | Loud; inverter models are quieter | Fans only | Runs outside the house |
| Runs for | As long as you refuel | Until the battery is empty | As long as gas supply lasts |
| Starts by itself | No | Instantly, as a battery | Yes, with an automatic transfer switch |
| Connect to the house | Cords, or a transfer switch fitted by an electrician | Plug appliances in | Professional install |
Questions
How do I work out what size generator I need?
Add the running watts of everything you want on at the same time. Then add the single largest start-up surge, because motors start one at a time. Add about 20% headroom to the running total so the generator isn't flat out.
What size generator do I need to run a house?
Champion puts a typical 2,000 sq ft home at 5,000 to 7,500 watts for the essentials. Central air, an electric water heater or an electric dryer push you to a standby generator, which Champion sells from 8,500 to 26,000 watts.
Will a 3,500-watt generator run a refrigerator?
Yes. A refrigerator needs up to 400 running watts plus 1,200 watts for a moment to start, so 1,600 watts at start-up. That leaves room for lights, Wi-Fi and a TV.
What is the difference between starting and running watts?
Running watts are what an appliance draws once it's going. Starting watts are the short extra burst a motor needs to get moving, such as a fridge compressor or a pump. A generator lists both, and you need to stay under both.
Can I use a power station instead of a generator?
For small loads, yes. A fridge alone uses about 1,400 Wh a day, so you'd want a power station of about 1,980 Wh to cover 24 hours. Pumps, heaters and air conditioning drain a battery fast, which is where a generator wins.
Does running on propane change the size I need?
Yes. Generators make less power on propane. Champion's 7500W dual-fuel model drops from 7,500 to 6,750 running watts on propane. Set the fuel to propane under Advanced and the model list uses propane ratings.
Can I run a generator in my garage?
No. The CDC says to run a generator outdoors only, more than 20 feet from windows, doors and vents, and never inside a home or garage, even with the door open. Use a battery-powered carbon monoxide alarm indoors.
Do I need a transfer switch?
To power hardwired circuits such as a well pump, furnace or sump pump without extension cords, yes. Champion recommends having a transfer switch installed by a licensed electrician.
Sources
- Champion Power Equipment, Generator Wattage Chart
- Champion Power Equipment, What Size Generator Do I Need?
- ENERGY STAR certified refrigerators and freezers, median annual energy use
- U.S. Department of Energy, Estimating Appliance Energy Use
- CDC, Carbon Monoxide Poisoning
- Model specs: each manufacturer's product page, linked in the table above