Best overall
Honda EU2200i
2,200W start · 1,800W run
Gasoline · Inverter · 48–57 dBA · 47 lb
The benchmark quiet inverter — legendary engine reliability and clean power (<3% THD) for sensitive electronics.
Check price on AmazonFree sizing tool — no signup
Generator Size Calculator
Pick the appliances you want to run — get the exact wattage and generator size you need, with real starting-watt surge math built in.
- 47 appliances
- Running + starting watts per item
- Brand-neutral — no manufacturer pays us
- No email required
Short answer
To size a generator, add the running watts of everything you'll run at once, then add the starting (surge) watts of the largest motor — a fridge or AC can surge 2–3× its running watts. A fridge, a few lights, and a TV need about a 3,000–4,000W generator; running a whole house often needs 10,000W or more.
Fridge
~700W run
~2,200W start
Surge
2–3×
motor start
Essentials
3–5 kW
fridge + lights
Whole house
10 kW+
standby
Carbon monoxide kills. Generator exhaust contains carbon monoxide (CO), which can be deadly in minutes. Run generators outdoors only, at least 20 feet from your home, with the exhaust pointed away from windows, doors, and vents. Never run a generator inside a house, garage, basement, shed, or RV — even with doors or windows open.
Estimates based on typical appliance wattages, not your specific model. Always confirm against your appliance nameplates and consult a licensed electrician before sizing a standby generator installation.
Recommended generators by size class
Real, widely available units we’d shop for in each size class. As an Amazon Associate, VyzeApps earns from qualifying purchases. Picks are chosen independently on merit — commission never decides what we recommend.
Recreational / portableUp to 3,500W
Best value
Westinghouse iGen2200
2,200W start · 1,800W run
Gasoline · Inverter · 52 dBA · excellent fuel economy
Matches the Honda’s 1,800W running output for a fraction of the price, and sips even less fuel.
Check price on AmazonBudget pick
Champion 2500W Inverter (201317)
2,500W start · 1,850W run
Gasoline · Inverter · 53 dBA · CO Shield · 40 lb ultralight
The easy-to-carry budget inverter — 40 lb, up to 11.5 hr runtime, with a built-in carbon-monoxide shutoff sensor.
Check price on AmazonMidsize portable3,500 – 8,500W
Best overall
Westinghouse iGen5000
5,000W start · 3,900W run
Gasoline · Inverter · 52 dBA · remote start · RV-ready TT-30R
Quiet enough for a campground and strong enough to start a 30-amp RV air conditioner.
Check price on AmazonBest value
Westinghouse WGen7500
9,500W start · 7,500W run
Gasoline · Remote start · transfer-switch ready (L14-30R)
Serious home-backup wattage — enough for essentials circuits via a transfer switch — at a midsize price.
Check price on AmazonQuietest
Champion 6250W Open Frame Inverter (100519)
6,250W start · 5,000W run
Gasoline · Open-frame inverter · 69 dBA · <3% THD
50% quieter and 20% lighter than a conventional 5,000W unit, with inverter-clean output.
Check price on AmazonLarge portable8,500 – 12,000W
Best overall
Westinghouse WGen9500DF
12,500W start · 9,500W run
Dual fuel (gas / propane) · Remote-start fob · L14-30R + 14-50R outlets · 74 dBA
12,500W of surge capacity with transfer-switch-ready outlets — a proven whole-panel backup workhorse.
Check price on AmazonBest value
DuroMax XP13000EH
13,000W start · 10,500W run
Dual fuel (gas / propane) · Electric start · 500cc engine · 74 dBA
More peak wattage per dollar than anything else in the class, on gas or propane.
Check price on AmazonHome standby12,000W and up
Best overall
Generac Guardian 22kW (7043)
22,000W start · 19,500W run
Propane / natural gas · Auto-transfer in ~10s · Wi-Fi Mobile Link monitoring
The most widely installed home standby generator, backed by the largest dealer and service network. 22kW on LP, 19.5kW on natural gas.
Check price on AmazonQuietest
Kohler 20RCAL
20,000W start · 18,000W run
Propane / natural gas · Command PRO engine · 200A transfer switch · corrosion-proof enclosure
Premium build quality and a corrosion-proof enclosure — a favorite for noise-sensitive and coastal installs. 20kW on LP, 18kW on natural gas.
Check price on AmazonStandby units are permanently installed and must be sized and fitted by a licensed electrician.
How this calculator works
Most generator calculators just add up wattage numbers. That misses the one thing that actually determines whether a generator can handle your appliances: the starting watt surge. Motors — in refrigerators, well pumps, air conditioners, and power tools — briefly draw 2-3x their running wattage for a fraction of a second when they switch on.
This calculator adds your total running watts (everything you selected, running steady) to the single largest starting-watt spike among those appliances — because in real use, appliances don’t all surge at the exact same instant. That combined number is your true peak load, which we then round up to the nearest common generator size class.
Appliance wattage reference
Typical running and starting watts by category. Switch categories to check any appliance — these are industry-typical averages, so always confirm your specific appliance’s nameplate for exact figures.
| Appliance | Running | Starting |
|---|---|---|
| Refrigerator / Freezer | 700W | 2,200W |
| Chest / Upright Freezer | 500W | 1,500W |
| Microwave (1000W) | 1,000W | 1,000W |
| Dishwasher | 1,500W | 1,500W |
| Coffee Maker | 1,000W | 1,000W |
| Toaster / Toaster Oven | 1,200W | 1,200W |
| Electric Range (per burner) | 2,100W | 2,100W |
| Electric Oven | 3,000W | 3,000W |
| Instant Pot / Slow Cooker | 700W | 700W |
| Appliance | Running | Starting |
|---|---|---|
| Washing Machine | 1,200W | 2,300W |
| Electric Clothes Dryer | 5,400W | 5,400W |
| Gas Clothes Dryer (motor only) | 700W | 1,800W |
| Clothes Iron | 1,200W | 1,200W |
| Appliance | Running | Starting |
|---|---|---|
| Window AC — 6,000 BTU | 700W | 2,200W |
| Window AC — 10,000 BTU | 1,200W | 3,600W |
| Central AC — per ton | 1,500W | 4,500W |
| Furnace Blower Fan (1/2 HP) | 800W | 2,350W |
| Electric Space Heater | 1,500W | 1,500W |
| Well Pump (1/2 HP) | 1,000W | 2,000W |
| Well Pump (1 HP) | 2,000W | 3,000W |
| Sump Pump (1/3 HP) | 800W | 1,300W |
| Sump Pump (1/2 HP) | 1,050W | 2,150W |
| Sewage Ejector Pump (1/2 HP) | 1,050W | 3,000W |
| Electric Water Heater (tank) | 4,000W | 4,000W |
| Appliance | Running | Starting |
|---|---|---|
| LED TV (up to 55") | 150W | 150W |
| Laptop / Desktop Computer | 300W | 300W |
| WiFi Router / Modem | 20W | 20W |
| LED Light Bulb (each) | 15W | 15W |
| Ceiling Fan | 75W | 75W |
| Box / Stand Fan | 200W | 200W |
| Garage Door Opener (1/2 HP) | 550W | 1,100W |
| CPAP Machine | 90W | 90W |
| Phone / Device Charger | 20W | 20W |
| Appliance | Running | Starting |
|---|---|---|
| Circular Saw (7-1/4") | 1,400W | 2,300W |
| Table Saw | 1,800W | 4,500W |
| Miter Saw (10") | 1,800W | 2,400W |
| Air Compressor (1.5 HP) | 1,500W | 3,000W |
| Angle Grinder | 1,200W | 2,400W |
| Power Drill (1/2") | 600W | 900W |
| Reciprocating Saw | 960W | 1,200W |
| Shop Vac / Wet-Dry Vac | 1,000W | 2,000W |
| Appliance | Running | Starting |
|---|---|---|
| RV Rooftop AC — 13,500 BTU | 1,500W | 3,500W |
| RV Rooftop AC — 15,000 BTU | 1,700W | 4,200W |
| RV Refrigerator | 600W | 2,000W |
| RV Microwave | 1,000W | 1,000W |
| RV Electric Water Heater | 1,500W | 1,500W |
| RV Converter / Battery Charger | 300W | 300W |
Standard generator sizes & classes
| Generator size | Class |
|---|---|
| 2,000 W | Recreational / portable |
| 3,000 W | Recreational / portable |
| 3,500 W | Recreational / portable |
| 4,000 W | Midsize portable |
| 5,000 W | Midsize portable |
| 6,500 W | Midsize portable |
| 7,500 W | Midsize portable |
| 8,500 W | Midsize portable |
| 10,000 W | Large portable |
| 12,000 W | Large portable |
| 15,000 W | Home standby |
| 20,000 W | Home standby |
| 24,000 W | Home standby |
The standard size classes portable and standby generators are sold in. The calculator recommends the smallest class that covers your peak surge watts.
How we calculate this
Every number on this page comes from the same sizing math the calculator runs — real surge math, not just a sum of nameplate watts:
- Total running watts. the sum of every selected appliance's running watts × its quantity — the steady load the generator carries.
- Largest surge delta. for each appliance, starting watts − running watts is the extra it needs the instant its motor kicks on. Only the single largest delta is added, because in practice one motor starts at a time while the rest run steady.
- Peak surge watts. total running watts + the largest surge delta — the load the generator must survive.
- Recommended size. the smallest standard generator class (2,000–24,000 W ladder above) at or above the peak surge watts.
Assumptions
- Appliance wattages are industry-typical averages — always check your model's nameplate or manual.
- One motor-driven appliance starts at a time; simultaneous compressor starts need a larger unit or a soft-start kit.
- Sustained loads should stay under ~90% of rated watts; altitude and heat derate output.
Sources
Last reviewed: July 13, 2026
Frequently asked questions
What size generator do I need for my house?
It depends entirely on which appliances you plan to run at the same time. Add up the running watts of everything you want powered, then add the starting (surge) watts of whichever single appliance has a motor that kicks on hardest — usually a refrigerator, well pump, or AC unit. Use the calculator above to get an exact number for your specific appliances instead of a generic house-size average.
What's the difference between running watts and starting watts?
Running watts is the power an appliance needs continuously once it's on. Starting (or surge) watts is a short spike some appliances need for a fraction of a second to get their motor moving — compressors, pumps, and power tools can need 2-3x their running wattage just to start. Resistive loads like heaters, toasters, and lights don't have this spike; their starting and running watts are the same.
Can I run my refrigerator and air conditioner at the same time on a portable generator?
Usually yes, as long as your generator can cover the combined running watts of both PLUS the starting watts of whichever one surges — and in practice only one motor surges at a time, since they don't start in the exact same instant. That's exactly what this calculator computes: total running watts plus the single largest starting-watt spike among your selected appliances.
How much bigger should my generator be than my calculated wattage?
The recommendation above already rounds up to the next common generator size class, which builds in headroom. If you plan to add more appliances later, or you live somewhere with frequent long outages, sizing up one class further gives you more comfortable margin and reduces wear on the generator from running near its limit.
Do I need a whole-house standby generator or a portable one?
Portable generators (2,000W-10,000W) cover a selection of essentials — fridge, some lights, a window AC, charging devices — and are far cheaper. Whole-house standby generators (10,000W-20,000W+) are hardwired and can run everything including central AC, but cost significantly more and need professional installation. This calculator works for sizing either — just select every appliance you want covered.
Can I run a generator indoors or in a garage?
No — never. Generator exhaust contains carbon monoxide (CO), an odorless, invisible gas that can kill in minutes. Running a generator inside a house, garage, basement, shed, or RV is deadly even with doors and windows open. Always run generators outdoors, at least 20 feet from your home, with the exhaust pointed away from windows, doors, and vents — and install battery-powered CO alarms inside the house as a second line of defense.
Popular sizing guides
What will a generator run?By size — 2,000W up to 15,000WGenerator size by applianceFridge, well pump, RV AC, CPAP & moreWhat size generator for a house?By square footage or bedroom countGenerator for a 2,000 sq ft houseOutage essentials, sized honestlyWhat will a 5,000-watt generator run?Midsize portable capacity, explainedWhat will a 7,500-watt generator run?Home-backup essentials via a transfer switchGenerator for a refrigerator700W running · 2,200W starting surgeGenerator for a well pumpSizing for the biggest motor surge in the house