What size generator do you need?
For the essentials you need about 222 running watts and 972 starting watts. Pick everything you want running at once and the calculator sizes the generator, on gasoline or propane, with matched models from Champion, Honda, Westinghouse and DuroMax.
- Free, no email. Every result shows its maths.
- Specs from each maker’s own product page, checked 16 October 2026.
- Uses the standard sizing rule: running watts plus the single biggest start-up.
- Flags 240 V loads that need a transfer switch.
What size generator do common plans need?
Each row is the calculator run on gasoline. Open any row to change it to your own list or switch to propane.
| Plan | Running | Starting | Calculator’s pick | |
|---|---|---|---|---|
| Essentials: fridge, lights, Wi-Fi, phones | 222 W | 972 W | Honda EU2200i | Open this plan |
| Essentials plus a gas furnace fan | 722 W | 1,472 W | Honda EU2200i | Open this plan |
| Essentials, furnace fan and sump pump | 1,522 W | 2,272 W | Champion 2500W Dual Fuel Inverter | Open this plan |
| Essentials, freezer and a well pump 240 V | 1,322 W | 2,322 W | Champion 6500W Dual Fuel Inverter | Open this plan |
| Window AC, fridge, lights and Wi-Fi | 1,402 W | 2,602 W | Honda EU3200i | Open this plan |
| Essentials plus microwave and coffee maker | 1,922 W | 2,672 W | Honda EU3200i | Open this plan |
| Central AC with the essentials 240 V | 3,722 W | 6,222 W | Champion 6500W Dual Fuel Inverter | Open this plan |
| Essentials, well pump and electric water heater 240 V | 5,722 W | 6,722 W | Champion 8500W Dual Fuel Inverter | Open this plan |
| RV: air conditioner and fridge | 1,980 W | 2,980 W | Honda EU3200i | Open this plan |
How do the 9 generators compare?
Sorted by running watts. “Runtime” is the maker’s own figure for a full tank of gasoline at a quarter load.
| Generator | Type | Gasoline (running / starting) | Propane | Outlets | CO shut-off | Weight | Runtime, 25% load |
|---|---|---|---|---|---|---|---|
| Honda EU2200i | Inverter | 1,800 / 2,200 W | gasoline only | 120 V | Yes | 47 lb | 8.1 h |
| Champion 2500W Dual Fuel Inverter | Inverter | 1,850 / 2,500 W | 1,665 / 2,500 W | 120 V | Yes | 39 lb | 11.5 h |
| Honda EU3200i | Inverter | 2,600 / 3,200 W | gasoline only | 120 V | Yes | 59 lb | 8.6 h |
| Champion 4500W Dual Fuel Inverter | Inverter | 3,250 / 4,500 W | 2,925 / 4,500 W | 120 V + RV TT-30 | Yes | 52 lb | 10 h |
| Westinghouse iGen5000DF | Inverter | 3,900 / 5,000 W | 3,500 / 4,500 W | 120 V + RV TT-30 | No | 105 lb | 18 h |
| Champion 6500W Dual Fuel Inverter | Inverter | 5,250 / 6,500 W | 4,725 / 6,500 W | 120/240 V (L14-30) | Yes | 105 lb | 15 h |
| Champion 8500W Dual Fuel Inverter | Inverter | 7,000 / 8,500 W | 6,300 / 8,500 W | 120/240 V (L14-30) | Yes | 214 lb | 14 h |
| Westinghouse WGen9500DFc | Open frame | 9,500 / 12,500 W | 8,500 / 11,200 W | 120/240 V (L14-30) | Yes | 212 lb | 12 h |
| DuroMax XP13000EH | Open frame | 10,500 / 13,000 W | 10,000 / 12,500 W | 120/240 V (L14-30) | Yes | 234 lb | 17 h |
Specs from each manufacturer’s product page, checked 16 October 2026. Noise figures are left out because makers measure them in different ways.
Questions people ask before buying
What size generator do I need for a power outage?
For the essentials (fridge, lights, Wi-Fi and phones) you need about 222 running watts and 972 starting watts, which a small 1,800 W generator covers. Add a gas furnace fan and it rises to 722 W running and 1,472 W starting. Central air is the big jump: about 3,722 W running and 6,222 W to start, and some central units need far more to start (Generac quotes up to 15 kW for a 3-ton system); a soft-start kit fitted by an HVAC technician lowers it.
What is the difference between running and starting watts?
Running watts are what a generator can supply continuously. Starting watts are a short burst it can give for a second or two while a motor (fridge, pump, AC) spins up. Add up the running watts of everything that runs at once, then add only the single biggest start-up extra, because motors start one at a time.
How many watts does a refrigerator need on a generator?
A typical fridge runs at about 150 W but needs around 900 W for a moment when the compressor starts. Honda's wattage guide lists an Energy Star fridge at up to 1,200 W starting, so check the label on yours.
Can a portable generator run a well pump?
Yes, if it has a 240 V outlet when the pump needs one. A 1/2 hp well pump runs at about 1,000 W and needs up to 2,000 W to start. With a fridge, freezer and the essentials that comes to about 1,322 W running and 2,322 W starting.
Does propane give less power than gasoline?
Yes. Across the dual-fuel models here, running watts are on average about 9% lower on propane, so size from the propane figures if that is what you will burn. Propane stores for years without going stale, which gasoline does not.
Inverter or open-frame generator?
Inverter generators are quieter, more fuel-efficient at light loads and give clean power for electronics, but cost more per watt. Open-frame generators give the most watts for the money and suit heavy loads like well pumps and central air.
Do I need a transfer switch?
Only if you want to power circuits in your home's wiring, such as a hard-wired well pump or furnace. That needs a transfer switch or interlock installed by a licensed electrician. Never plug a generator into a wall outlet; for anything else, use heavy-duty outdoor extension cords.
Where should I put a generator?
Outdoors only, at least 20 feet from your home, with the exhaust pointed away from any building, as the U.S. Consumer Product Safety Commission advises. Never run one in a garage, basement or shed, and keep battery carbon monoxide alarms on every level of the home.
Generator or power station?
A battery power station is silent, needs no fuel and is safe indoors, so it suits essentials for an evening or a day. A generator is the better fit for heavy loads (well pumps, AC, electric heat) and for outages that last several days.
Rather run it silently indoors?
For an evening or a day of essentials, a battery power station may be enough. Size a power station or build a full outage plan with water, food and a checklist.
