Generator sizing
Generator Wattage Chart
Choose generator size by adding the running watts for everything you need powered at the same time, then adding the largest starting-watt surge for a motor, compressor, pump, or AC unit. This chart gives planning ranges for common household loads before you use the exact generator size calculator.
Appliance starting watts and running watts
| Appliance | Running watts | Starting watts | Sizing note |
|---|---|---|---|
| Refrigerator | 700 W | 1,200 to 2,200 W | Allow extra surge for compressor startup. |
| Freezer | 500 W | 1,000 to 2,000 W | Chest and upright freezers vary by age and size. |
| Sump pump | 800 to 1,500 W | 1,500 to 3,000 W | Startup surge can be the deciding load during storms. |
| Microwave | 1,000 to 1,500 W | 1,000 to 1,500 W | Usually a short high-running load. |
| Window AC | 600 to 1,500 W | 1,200 to 3,000 W | BTU size and compressor startup matter. |
| Central AC | 3,000 to 5,000 W | 6,000 to 12,000 W | Often needs a large generator or soft-start equipment. |
| Furnace blower | 400 to 800 W | 800 to 1,600 W | Gas heat still needs electricity for the blower and controls. |
| Well pump | 750 to 1,500 W | 1,500 to 4,000 W | Check pump horsepower and control box ratings. |
| Lights | 50 to 600 W | 50 to 600 W | LED lighting can keep this load small. |
| TV | 75 to 250 W | 75 to 250 W | Large TVs and sound systems use more. |
| Router | 10 to 30 W | 10 to 30 W | Small load, but useful during outages. |
| Laptop | 45 to 100 W | 45 to 100 W | Charging load depends on adapter size. |
| Space heater | 1,500 W | 1,500 W | High running load; avoid combining with other large loads. |
Starting watts vs. running watts
Running watts are the steady load after an appliance is already operating. Starting watts are the short surge needed to start motors, compressors, pumps, and AC units. Generator sizing usually fails when the running load looks fine but the startup surge is too high.
For a safe estimate, add the running watts for the loads you want at the same time, add the single largest startup surge, then leave a margin for old equipment, cold weather, extension cords, and load changes.
How to choose generator size
- List only the appliances and circuits you actually need during an outage.
- Add their running watts.
- Add the largest starting-watt surge from a pump, refrigerator, freezer, AC, or blower.
- Round up instead of running the generator at its limit.
- Confirm the generator outlet, transfer switch, fuel type, ventilation, and carbon monoxide safety requirements.
Example generator sizes
2000 watt generator
Good for a refrigerator, a few lights, router, laptop, TV, and one small extra load. It is usually not enough for a sump pump plus microwave or large AC at the same time.
3500 watt generator
Can cover a refrigerator or freezer, lights, electronics, and one medium surge load such as a sump pump if other large appliances are staggered.
5000 watt generator
A practical emergency size for several essentials: refrigerator, freezer, furnace blower, lights, router, TV, and a sump pump with careful load management.
7500 watt generator
Often enough for broader household essentials and some well pumps or window AC units, but central AC startup may still exceed the generator rating.
10000 watt generator
Useful for larger outage plans, well pumps, multiple circuits, and some central AC setups, but exact sizing still depends on starting watts and transfer equipment.
FAQs
Generator wattage chart questions
What size generator do I need for a house?
Add the running watts for the appliances and circuits you want to use at the same time, then add the largest starting-watt surge. Many essential-load plans land around 5,000 to 7,500 watts, while whole-home plans can need 10,000 watts or more.
What is the difference between starting watts and running watts?
Running watts are the watts an appliance needs after it is operating. Starting watts are the short surge needed by motors, compressors, pumps, and some tools when they first turn on.
Can a 2000 watt generator run a refrigerator?
Often yes, if the refrigerator startup surge fits within the generator rating and you keep other loads small. Check the refrigerator label or meter reading before assuming it can start reliably.
Will a 7500 watt generator run central AC?
Sometimes, but not always. Central AC can have a very high compressor startup surge, so you need the equipment nameplate, locked-rotor or starting-watt estimate, and any soft-start equipment details.
Should I size a generator by watts or amps?
Use watts for generator sizing because appliance labels may use volts, amps, or watts. If you only have amps, multiply volts by amps to estimate watts, then account for starting surge.