Generator Wattage Calculator: Find the Right Size Generator

Size a portable generator by adding the running watts for everything you’ll run at the same time, then add only the single largest additional starting-watt surge. For most homeowners, that puts an essentials outage setup around 3,000-4,000 watts, a 30-amp RV around a 4,500W-class inverter, and central AC or most-of-house loads in 10,000+ watt territory.

Use the calculator below first, then sanity-check your result against the wattage chart and examples on this page. The goal is simple: enough starting capacity to handle motors, enough running capacity to avoid running the generator flat-out.

Wattage Calculator

Wattage Calculator

How Will You Primarily Use The Generator?

Step 1

Select an option below

EU7000-wattage-calculator-home
    Includes:
  • Home back up power
  • Primary home power
EU7000-wattage-calculator-work
    Includes:
  • Construction/Contractor
  • Rental fleet
  • Farm/Agricultural
EU7000-wattage-calculator-play
    Includes:
  • RV vehicle
  • Camping
  • Tailgating
  • Outdoor events

How to size a generator the right way

The standard portable generator sizing method comes from the Lowe’s/Generac wattage worksheet: list what runs together, total the running watts, then add the largest single starting surge. You can see the source worksheet here: portable generator wattage chart.

Here’s the method to use with the calculator above:

  1. List every device you’ll run at the same time and add up all running watts.
  2. Find the one device with the highest additional starting watts.
  3. Add that single starting-watt number to the running total. That gives you the starting, or surge, capacity your generator needs.

You don’t add every motor’s starting surge. Motors start intermittently, not all at once, so the worksheet method uses the largest single additional surge.

The worksheet’s own example shows the math clearly:

Load Running watts Additional starting watts
Refrigerator 700 2,200
Sump pump 1,050 2,150
Belt sander 1,200 2,400
Air compressor 1/2 HP 1,000 2,000
Total running watts 3,950 Use highest surge: 2,400

That setup needs 3,950 running watts and 6,350 starting watts. A generator rated below either number is undersized for that exact load plan.

Generator wattage chart: running and starting watts

Use this chart as a baseline, then check the nameplate on your appliance. The running watts and additional starting watts below are from the standard Lowe’s/Generac portable generator worksheet unless noted.

Appliance Running watts Additional starting watts
Refrigerator/Freezer 700 2,200
Sump pump 1/2 HP 1,050 2,150
Microwave, 1000W 1,000 0
Coffee maker 1,000 0
Space heater 1,800 0
Humidifier 175 0
Computer with 17" monitor 800 0
Box fan 100 0
Cell phone charger 25 0
AM/FM radio 100 0
RV air conditioner, 13,500 BTU 700 1,500
Circular saw 7-1/4" 1,400 2,300
Miter saw 10" 1,800 3,300
Table saw 10" 2,000 2,000
Air compressor 1 HP 1,400 3,600
Belt sander 1,200 2,400
Hand drill 1/2" 600 900
Airless paint sprayer 1/3 HP 600 1,200
Reciprocating saw 960 0
Halogen work light 1,000 0

The worksheet’s 27-inch TV figure is dated CRT-era data. A modern 55-inch LED TV usually draws roughly 60-120 watts, so use the LED number on your TV’s label instead of the old worksheet number.

Some loads vary too much by model to size from a generic chart alone:

  • Well pump 1 HP: about 1,000 running watts and 2,000-3,000 starting watts.
  • Furnace blower fan: about 500-800 running watts, roughly double to start.
  • Window AC: about 1,200 running watts and about 1,800 starting watts for a typical 10-12k BTU 120V unit.
  • Central AC, 3-ton: 10,000+ total watts, which usually means a large portable or a home standby generator.

Worked examples: what size generator do you need?

Essentials-only outage kit

This is the common fridge, fan, lights, TV, and charging setup. It’s the right target if you want food cold, phones charged, a little airflow, and basic comfort without trying to run the whole house.

Load Running watts Additional starting watts
Refrigerator/Freezer 700 2,200
4 LED bulbs 40 0
55" LED TV 100 0
Phone and laptop charging 90 0
Box fan 100 0
Total needed 1,030 Highest surge: 2,200

That comes out to about 1,030 running watts and about 3,230 starting watts. A 3,000-4,000W class generator covers it with headroom; start with our best 3000-watt generators guide if that’s your use case.

30-amp RV setup

A 30-amp RV plug is capped at 3,600 watts because 120V x 30A = 3,600 watts. That cap matters more than the biggest number printed on the generator box.

Load or limit Running watts Additional starting watts
30-amp RV plug limit 3,600 Not a surge rating
RV air conditioner, 13,500 BTU, worksheet figure 700 1,500
Many 13.5k BTU RV AC units in the real world 1,200-1,600 Check nameplate

A 13.5k BTU RV AC, fridge, converter, and a few small loads usually fit best under a 4,500W-class inverter. Real RV air conditioner draw varies a lot by model and age, so read the nameplate on your unit and use our 30-amp RV generator sizing guide before buying.

Jobsite saw and compressor pair

Power tools are where starting watts bite people. A compressor and saw may look manageable by running watts, but the compressor’s starting surge sets the generator size.

Tool Running watts Additional starting watts
Circular saw 7-1/4" 1,400 2,300
Air compressor 1 HP 1,400 3,600
Total needed 2,800 Highest surge: 3,600

The math is 2,800 running watts plus 3,600 additional starting watts, so the requirement is 6,400 starting watts. That points to a 6,500W+ class generator for this pair.

Most of the house, including central AC

Central air changes the whole sizing conversation. A 3-ton central AC can push you into 10,000+ total watts, and that usually means a large portable generator or a home standby setup.

If you’re trying to run most of the house, look at the best 12000-watt generator class and plan fuel storage before the storm. If propane is your backup fuel, use our generator propane use guide so you’re not guessing on runtime.

Starting watts vs running watts

Running watts are what an appliance needs after it’s already operating. Starting watts are the short burst a motor needs to get moving, and motors commonly need 2-3x their running watts to start.

Resistive loads are simpler. Space heaters, bulbs, and coffee makers don’t have a meaningful startup surge, so the worksheet lists 0 additional starting watts for those kinds of loads.

Sizing rules the spec sheets don’t spell out

Buy 20-25% more capacity than your calculated need. Running a generator flat-out is hard on the engine and leaves no room for the next load. A good target is to load it to about 80% continuous max.

Use the propane rating if you’ll run propane. Dual-fuel generators make about 10% fewer watts on propane than gasoline. If propane is your main fuel, size against the propane output, not the gasoline number.

Account for altitude. Small engines lose roughly 3% of output per 1,000 ft of elevation. If you camp or live at elevation, that loss comes straight out of your usable wattage.

Separate motor loads from resistive loads. Motors need surge capacity; heaters and coffee makers usually don’t. That’s why a fridge can be harder to start than its running watts suggest, while a space heater is just a steady heavy load.

Good generators for each size class

Use these as size-class examples after you run the calculator above. Match the generator’s running watts and starting watts to your actual load list, especially if you’ll be on propane or at elevation.

Small and quiet 2,000W class

Honda EU2200i: 1,800 running watts, 47 lb, and still the quiet benchmark for small inverter generators.

Check current price on Amazon →

Mid-size 4,500W dual-fuel class

Champion 200988: 3,500W on gas, 3,150W on propane, electric start, and RV-ready.

Check current price on Amazon →

Whole-home portable 12,000W class

DuroMax XP12000EH: 9,500W on gas, dual fuel, and 50-state legal for big outage loads.

Check current price on Amazon →

Full appliance wattage reference

These are compiled estimates; check your appliance’s nameplate label because actual draw varies by model, age, and startup behavior.

ApplianceMinimumMaximumStandby
100W light bulb (Incandescent)100W100W0W
22 Inch LED TV17W17W0.5W
25″ Color TV150W150WN/A
3″ belt sander1000W1000WN/A
32 Inch LED TV20W60W1W
42 Inch LED TV58W60W0.3W
42 Inch Plasma TV450W600WN/A
46 Inch LED TV60W70W1W
49 Inch LED TV85W85W1W
55 Inch LED TV116W116W0.5W
60W light bulb (Incandescent)60W60W0W
65 Inch LED TV120W130W1W
82 Inch LED TV228W295W0.5W
9″ disc sander1200W1200WN/A
Air Cooler65W80WN/A
Air Fryer1500W1500WN/A
Air Purifier25W30WN/A
Amazon Echo3W3W2W
Amazon Echo Dot2W3WN/A
Amazon Echo Show2W4W0.1W
American-Style Fridge Freezer40W80WN/A
Apple TV3W6W0.3W
Aquarium Pump20W50WN/A
AV Receiver450W450WN/A
Bathroom Towel Heater60W150WN/A
Ceiling Fan60W70W0W
Chromebook45W45WN/A
Chromecast2W2WN/A
Clock radio1W2WN/A
Clothes Dryer1000W4000WN/A
Coffee Maker800W1400WN/A
Computer Monitor25W30WN/A
Cooker Hood20W30W0W
Corded Drill600W850WN/A
Corded Electric Handheld Leaf Blower2500W2500WN/A
Cordless Drill Charger70W150WN/A
CPAP machine30W60WN/A
Curling Iron25W35W0W
DAB Mains Radio5W9WN/A
Deep Freezer19W19WN/A
Dehumidifier240W240WN/A
Desktop Computer100W450WN/A
Dishwasher1200W1500WN/A
Domestic Water Pump200W300W0W
DVD Player26W60WN/A
Electric Blanket200W200WN/A
Electric Boiler4000W14000WN/A
Electric Doorbell Transformer2W2WN/A
Electric Heater Fan2000W3000WN/A
Electric Kettle1200W3000W0W
Electric Mower1500W1500WN/A
Electric Pressure Cooker1000W1000WN/A
Electric Shaver15W20WN/A
Electric stove2000W2000WN/A
Electric Tankless Water Heater6600W8800WN/A
Electric Thermal Radiator500W500WN/A
Electric Toothbrush Charger6W6WN/A
Espresso Coffee Machine1300W1500WN/A
EV Car Charger2000W7000WN/A
EV Home Charger1600W3400WN/A
Evaporative Air Conditioner2600W2600WN/A
External Hard Drive1W3WN/A
Extractor Fan12W12WN/A
Fluorescent Lamp28W45WN/A
Food Blender300W400WN/A
Food Dehydrator800W800WN/A
Freezer30W50WN/A
Fridge100W220WN/A
Fridge / Freezer150W400WN/A
Fryer1000W1000WN/A
Game Console120W200WN/A
Gaming PC300W600W1W
Garage Door Opener300W400WN/A
Google Home Mini15W15W2W
Guitar Amplifier20W30WN/A
Hair Blow Dryer1800W2500WN/A
Hand Wash Oversink Water Heater3000W3000WN/A
Heated Bathroom Mirror50W100WN/A
Heated Hair Rollers400W400WN/A
Home Air Conditioner1000W4000WN/A
Home Internet Router5W15WN/A
Home Phone3W5W2W
Home Sound System95W95W1W
Hot Water Dispenser1200W1300WN/A
Hot Water Immersion Heater3000W3000WN/A
Humidifier35W40WN/A
iMac60W240W1W
Induction Hob (per hob)1400W1800WN/A
Inkjet Printer20W30WN/A
Inverter Air conditioner1300W1800WN/A
Iron1000W1000WN/A
Jacuzzi3000W7500W1500W
Kitchen Extractor Fan200W200WN/A
Laptop Computer50W100WN/A
Laser Printer600W800WN/A
Lawnmower1000W1400WN/A
LED Christmas Lights5W5WN/A
LED Light Bulb7W10W0W
LG Soundbar23W30W0.5W
Mi Box5W7W3W
Microwave600W1700W3W
Night Light1W1W0W
Nintendo Switch AC Adapter7W40WN/A
Outdoor Hot Tub60W500WN/A
Oven2150W2150WN/A
Paper Shredder200W220WN/A
Pedestal Fan50W60WN/A
Percolator800W1100WN/A
Philips Hue Smart Bulb8W9W0.4W
Phone Charger4W7WN/A
PlayStation 485W90WN/A
PlayStation 5160W200WN/A
Portable Air Conditioner1000W1200WN/A
Power Shower7500W10500W0W
Pressure Cooker700W700WN/A
Pressure Washer1500W1500WN/A
Projector220W270W1W
Refrigerator100W200WN/A
Rice Cooker200W800WN/A
Ring Spotlight Cam Wired25W4W2W
Sandwich Maker700W1000WN/A
Scanner10W18WN/A
Set Top Box27W30WN/A
Sewing Machine70W80WN/A
Singer Sewing Machine100W100WN/A
Slow Cooker160W180WN/A
Smoke Detector0W1WN/A
Space Heater2000W5000WN/A
Steam Iron2200W2500WN/A
Steriliser650W650WN/A
Straightening Iron75W300WN/A
Strimmer300W500WN/A
Submersible Water Pump200W400WN/A
Table Fan10W25WN/A
Table Top Fridge10W15WN/A
Tablet Charger10W15WN/A
Tablet Computer5W10WN/A
Toaster800W1800W0W
Tower Fan60W60WN/A
Treadmill280W900WN/A
Tube Light (1500mm)22W22WN/A
TV (19″ color)40W100W1W
Vacuum Cleaner450W900W0W
Wall Fan45W60W0W
Washing Machine500W500W1W
Water Dispenser100W100WN/A
Water Feature35W35WN/A
Water Filter and Cooler70W100WN/A
WiFi Booster1W2WN/A
WiFi Router4W10W4W
Window Air Conditioner500W1500WN/A
Wine cooler (18 bottles)83W83W0W
Xbox One50W110W14W

Bottom line

Use the calculator above, then follow the worksheet method: total the running watts and add the single largest additional starting surge. For a basic outage kit, a 3,000-4,000W class generator is usually enough; for a 30-amp RV, a 4,500W-class inverter is the sweet spot; for central AC or most-of-house loads, plan on 10,000+ watts.

Buy with 20-25% headroom, size against the propane rating if you’ll use propane, and account for altitude if it applies. That keeps the generator from living at full throttle and gives motor loads room to start cleanly.

Frequently asked questions

What size generator do I need for my house?

For essentials only, most homes land around 3,000-5,000 watts. That covers a refrigerator, lights, TV, charging, and a fan with room for startup surge. If you want most of the house with central AC, you’re usually in 10,000+ watt territory, and true whole-house coverage is often standby-generator territory.

What will a 4,500-watt generator run?

A 4,500-watt generator can run a basic essentials kit and often an RV AC or a typical window AC if you manage loads. For example, an essentials kit at about 1,030 running watts plus a typical window AC at about 1,200 running watts is about 2,230 running watts; adding the refrigerator’s 2,200-watt surge puts the starting need around 4,430 watts.

How many watts does a refrigerator need?

Per the standard Lowe’s/Generac worksheet, a refrigerator/freezer uses 700 running watts and needs about 2,200 additional watts to start. That means you size it as 700 running watts, but your generator must have surge capacity for the startup hit.

What size generator do I need for a 30-amp RV?

A 30-amp RV plug is limited to 3,600 watts because 120V x 30A = 3,600 watts. A 4,500W-class inverter is the common sweet spot because it can handle the RV AC startup surge while staying practical for camping.

Do I add up all the starting watts?

No. Add up all running watts, then add only the single largest additional starting-watt number. Motors start intermittently, not all at once, so adding every surge together oversizes the generator.

Can a generator be too big?

Yes. An oversized generator costs more, burns more fuel, makes more noise, and weighs more than necessary. Light loading can also glaze some engines, so a better target is sizing your normal load around 80% of the generator’s continuous capacity.

How much extra generator capacity should I buy?

A good rule of thumb is 20-25% more capacity than your calculated need. That gives you headroom for startup surge, altitude loss, propane derating, and the small loads people forget to count.

How we put this guide together: The sizing method and wattage figures on this page come from the industry-standard portable generator wattage worksheet (published by Lowe’s/Generac) and manufacturer spec sheets; the worked examples show the arithmetic so you can rerun it for your own loads. We don’t run a hands-on test lab; where we cite a runtime or spec, it’s the manufacturer’s published figure with the load level stated, and the math is shown so you can check it. As an Amazon Associate, Electric Ninjas earns from qualifying purchases made through links on this page.

Electric Ninjas was created by Jeremy Green to help people find the right portable generator for their needs.

Contact Information

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North Andover, MA 01845

Phone: 617-221-5915

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