To size a generator, add the running watts of everything you want to power at once, then make sure the generator's starting (surge) watts cover your largest motor load, and leave about 20% headroom. Most people buy too small because they forget that motors need a burst of extra power to start.
Step 1: List what you must run
Start with essentials, not everything you own. The running watts below are approximate typical values; always check the label on your own appliances.
| Appliance | Approx. running watts | Starting surge |
|---|---|---|
| Refrigerator or chest freezer | 100 to 200 | Often 2 to 3 times running |
| Sump pump (1/3 hp) | 700 to 1,000 | Roughly 2 times running |
| Well pump (1/2 hp) | 800 to 1,000 | Roughly 2 to 3 times running |
| Furnace fan | 400 to 800 | Roughly 2 times running |
| Microwave | 1,000 | Little |
| Space heater | 1,500 | Little |
| LED lights, phone chargers, router | 10 to 100 combined | None |
Step 2: Add up running watts, then find the biggest surge
Add the running watts of everything you will use at the same time. Then take the single largest surge need, since motors rarely all start at once. Your generator needs to cover total running watts plus the extra surge of the biggest motor.
Example: refrigerator (150 W running, about 450 W surge) + well pump (900 W running, about 2,000 W surge) + lights and chargers (150 W). Running total is 1,200 W. Add the biggest extra surge (about 1,100 W for the pump) and you need roughly 2,300 W of starting capacity. With 20% headroom, a generator rated for about 3,000 starting watts is a safe choice.
Step 3: Choose inverter or conventional
| Inverter generator | Conventional generator | |
|---|---|---|
| Power quality | Clean, stable power; safe for laptops and electronics | Fine for tools and motors; more voltage variation |
| Noise | Much quieter | Louder |
| Fuel use | Adjusts engine speed, uses less fuel at light loads | Runs at a fixed speed |
| Price per watt | Higher | Lower |
| Best for | Camping, electronics, home backup of small loads | Large loads, job sites, whole-house backup |
Safety rules that matter
- Run generators outdoors only, far from doors, windows and vents. The U.S. Consumer Product Safety Commission advises keeping them at least 20 feet from the home.
- Never plug a generator into a wall outlet. To power home circuits, have an electrician install a transfer switch or interlock.
- Let it cool before refueling, and store fuel safely.
- Install battery-powered carbon monoxide alarms.
Generators to compare
These are examples from our shop. Match the starting-watt rating to your worksheet, not just the headline number.
- TMG Industrial 7250 Watt digital inverter hybrid generator, dual fuel (gas or LPG)
- TMG Industrial 10500 Watt digital inverter hybrid generator, tri-fuel (gas, LPG or natural gas)
For smaller loads such as a fridge, lights and phone charging, a portable power station may be all you need. Browse Generators & Inverters for the full range, and read Solar vs. Generator if you are still deciding between the two.
Frequently asked questions
Can a 2,000 watt generator run a refrigerator?
Usually yes, since most refrigerators need a few hundred watts including startup, leaving room for lights and electronics.
How long will a generator run on one tank?
It depends on load. Check the rated runtime at 50% load in the product specs.
Should I get a power station instead?
For small loads and indoor use, a power station is quiet and fuel-free. For long runs and large loads, a generator gives more output.
What does dual fuel mean?
A dual fuel generator can run on gasoline or propane (LPG), which is useful because propane stores far longer than gasoline.
