Running watts vs. starting watts
The single most misunderstood concept in generator sizing — and the reason so many people buy the wrong unit.
Running watts
Running watts (sometimes called rated or continuous watts) is the steady power an appliance draws while operating normally. A refrigerator might run on 150 watts once its compressor is up to speed.
Starting watts
Starting watts (surge or peak watts) is the brief spike an appliance demands at the instant it switches on. Anything with a motor or compressor — fridges, pumps, air conditioners — needs two to three times its running watts for a fraction of a second to overcome inertia. That same 150-watt fridge can demand 450 watts the moment its compressor starts.
Why it matters
A generator has two ratings: continuous output and surge output. If your appliances' combined startup demand exceeds the generator's surge rating, the unit trips or stalls — usually at the worst possible moment, in the dark, during a storm. Sizing only by running watts is the classic mistake.
The numbers, by appliance
| Appliance | Running | Starting (peak) |
|---|---|---|
| Refrigerator | 160W | 480W |
| Chest freezer | 200W | 600W |
| Central AC (3-ton) | 3500W | 12600W |
| Window AC (12k BTU) | 1300W | 3380W |
| Heat pump (3-ton) | 4000W | 14400W |
| Furnace blower fan | 600W | 1560W |
| Well pump (1/2 HP) | 1000W | 3000W |
| Sump pump (1/3 HP) | 800W | 2080W |
| Dishwasher | 1300W | 2600W |
| Washing machine | 1000W | 2600W |
| Electric dryer | 3000W | 6000W |
| Medical refrigerator | 200W | 600W |
| Garage door opener | 550W | 1430W |
| Power tools | 1000W | 2600W |
| Central AC (2-ton) | 2400W | 8640W |
| Central AC (5-ton) | 5800W | 20880W |
| Window AC (8k BTU) | 715W | 1859W |
| Window AC (15k BTU) | 1600W | 4160W |
| Mini-split (12k BTU) | 1100W | 2860W |
| Portable AC (12k BTU) | 1200W | 3120W |
| Well pump (1 HP) | 2000W | 6000W |
| Well pump (3/4 HP) | 1500W | 4500W |
| Sump pump (1/2 HP) | 1050W | 2730W |
| Pool pump (1.5 HP) | 1800W | 4680W |
| Refrigerator (large/side-by-side) | 250W | 750W |
| Mini-fridge | 90W | 270W |
| Garbage disposal | 500W | 1300W |
| Gas dryer (electric controls) | 700W | 1400W |
| Air compressor (portable) | 1500W | 3900W |
| Table saw | 1800W | 4680W |
| RV rooftop AC (13.5k BTU) | 1300W | 3380W |
| Oxygen concentrator | 350W | 700W |
See the full method on our methodology page, or jump straight to the load sizer.