Add Your Loads
Set a quantity for everything that could run at the same time. Add your own load at the bottom if it is not listed.
Kitchen
Essentials
Comfort
Laundry
Jobsite
Custom load
Typical Appliance and Tool Wattage
| Load | Running Watts | Starting Watts |
|---|---|---|
| Refrigerator | 700 | 2,200 |
| Chest freezer | 500 | 1,500 |
| Microwave (1,000W) | 1,500 | — |
| Coffee maker | 1,000 | — |
| Electric range burner (one) | 1,500 | — |
| Sump pump (1/3 HP) | 800 | 1,300 |
| Sump pump (1/2 HP) | 1,050 | 2,150 |
| Well pump (1/2 HP) | 1,000 | 2,100 |
| Well pump (1 HP) | 2,000 | 4,000 |
| Furnace fan (1/2 HP) | 800 | 2,350 |
| LED lights (10 bulbs) | 100 | — |
| Wi-Fi router + modem | 30 | — |
| TV (55" LED) | 150 | — |
| Laptop | 60 | — |
| CPAP machine | 60 | — |
| Window AC (10,000 BTU) | 1,200 | 3,600 |
| Central AC (3-ton) | 3,500 | 10,500 |
| Space heater | 1,500 | — |
| Electric water heater | 4,500 | — |
| Washing machine | 1,150 | 2,250 |
| Electric dryer | 5,400 | 6,750 |
| Gas dryer | 700 | 1,800 |
| Circular saw (7-1/4") | 1,400 | 2,300 |
| Miter saw (10") | 1,800 | 2,800 |
| Air compressor (1 HP) | 1,600 | 4,500 |
| Table saw (10") | 1,800 | 4,500 |
| Drill (1/2") | 600 | 900 |
| Battery charger (tool) | 100 | — |
| Work light (halogen 500W) | 500 | — |
| Shop vac (5 HP peak) | 1,100 | 1,600 |
Starting watts shown as the total draw for the first second or two of a motor start. Resistive loads (heaters, toasters, incandescent and LED lights) have no start surge. Your equipment nameplate or manual gives the real number.
How to Size a Generator
Generators are rated two ways. Running (rated) watts is what the generator can supply continuously. Starting (surge or peak) watts is the short burst it can deliver for a second or two while motors spin up. You need enough of both.
- List everything that could run at the same time and add up their running watts.
- Find the one motor load with the biggest start surge, and add its extra starting watts (starting minus running) on top of the total. Only one motor usually starts at a time, so you only add the biggest surge.
- Pick a generator whose running watts cover the total with about 20% headroom, and whose starting watts cover the peak.
Example: refrigerator (700 run / 2,200 start), sump pump (1,050 / 2,150), furnace fan (800 / 2,350), lights and router (130). Running total is 2,680 W. The biggest extra surge is the furnace fan at 1,550 W, so the peak is 4,230 W. With 20% headroom you want about 3,200 running watts and at least 4,300 starting watts, which puts you in the 3,500–4,500 W class.
Why Headroom Matters
Running a generator at 100% for hours shortens its life, drops voltage, and leaves no room for a second motor kicking on. Fuel economy is best at around 50–75% load. Altitude and heat also reduce output; most engines lose roughly 3% of power for every 1,000 feet above sea level.
Inverter vs Conventional Generators
Inverter generators produce clean, stable power that is safe for laptops, TVs and modern furnace control boards, and they throttle down at light loads to save fuel and noise. Conventional open-frame generators give more watts per dollar and handle big motor starts well, which is why they are common on jobsites. Many newer conventional units are rated for sensitive electronics, but check the total harmonic distortion spec (under 5% is the target).
240V Loads and Home Hookup
Well pumps, central AC, electric dryers, ranges and water heaters often run on 240 volts. Your generator needs a 240V outlet (an L14-30 or 14-50 receptacle) to run them, and the house needs a properly installed transfer switch or panel interlock. Never backfeed a dryer outlet with a double-male cord; it can energize the utility line and kill a lineworker.
Jobsite Sizing
On a jobsite, the air compressor and table saw are the hard starters. A 1 HP compressor can pull 4,000+ watts at start. If two crews will run saws and a compressor off one generator, size for the compressor surge plus everything else running. A 5,000–7,500 W conventional unit covers most residential framing and trim crews. Use the shortest, heaviest extension cords you can; long thin cords drop voltage and make motors work harder.
Whole-House Standby
Permanently installed standby generators (typically 14–26 kW) run on natural gas or propane and switch on automatically. Sizing for these follows a load calculation like the one an electrician uses for a service upgrade. See our electrical load calculator for that method.
Frequently Asked Questions
For essentials (refrigerator, freezer, sump or well pump, furnace fan, lights, Wi-Fi) most homes need 5,000–7,500 running watts. Add central air or an electric water heater and you move to 10,000–15,000 watts or a whole-house standby unit.
A refrigerator runs on about 700 watts but needs around 2,200 watts to start. A 2,500–3,000 W generator handles a fridge plus a few lights. Add other loads and size up.
No. Add all the running watts, then add only the largest single extra start surge. Motors rarely start at the exact same moment, so stacking every surge would oversize the generator.
Usually yes for a 10,000 BTU unit, which runs near 1,200 W and starts near 3,600 W, but there is little room left for anything else while it starts. A soft-start kit on the AC lowers the surge.
Not always, but inverter generators deliver cleaner power with low harmonic distortion, which protects electronics. Conventional generators rated under 5% THD are also generally safe.
