What size generator do I need? In 2026 the honest answer is: it depends on your home more than it ever has. Ten years ago a typical house had a gas furnace, a refrigerator and perhaps one air conditioner. Today the same street has heat pumps, induction ranges, electric vehicle chargers and home offices full of electronics. A sizing rule that worked in 2015 can be far off now.
The good news is that the method has not changed. You add up what must run, allow for motors starting and leave some room. What has changed is the list of loads, and the tools you have for shrinking them.
This guide gives you a 2026 sizing chart by home type and then works through six real-world examples, from an apartment to an all-electric house with an EV. It also explains three things older guides leave out: modern high-draw loads, soft starters and load management, and how fuel and altitude cut a generator’s real output. The wattages are typical planning values. We have not tested these generators.
Generator sizing in 2026 at a glance
Running watts, plus the biggest start, plus 20%
Appliance figures are typical planning values. Generator figures are from makers’ pages, checked October 2026.
Quick answer
Add the running watts of everything that must run at the same time. Add the extra starting watts of the largest motor once. Multiply the running total by 1.2. For most homes, essentials need 3,500 to 7,500 running watts from a portable generator. A whole home with central air usually needs a 14 to 22 kW standby generator. Then adjust: allow about 10% less on propane, about 3.5% less per 1,000 feet of altitude, and never plan to charge an electric vehicle at full speed from a generator.
How we put this guide together
We have not tested these generators. Appliance wattages are typical planning values in line with commonly published charts, and they match the ones in our original sizing guide and our calculator. Derating figures come from Champion’s and Kohler’s published manuals and spec sheets. EV charger figures are simple arithmetic and match Generac’s published charger specifications. Generator figures come from makers’ pages and Amazon listings, checked in October 2026. For a standby generator, a dealer’s load assessment at your home is the final word.
In this guide
- The Method in Four Steps
- The 2026 Wattage Chart
- The 2026 Sizing Chart by Home Type
- Six Worked Examples
- Two Tools That Shrink the Generator You Need
- Three Things That Cut a Generator’s Real Output
- Voltage and Outlets: The Check People Skip
- Measure Instead of Guessing
- One Generator for Each Example
- Portable or Standby: Where the Line Falls in 2026
- Common Generator Sizing Mistakes (and the Fix)
- Pro Tips for Sizing in 2026
- Real-Life Scenarios: What Size Would You Pick?
- What Size Generator Do I Need: FAQ
- Your 2026 Generator Sizing Checklist
The Method in Four Steps
If you only read one section, read this one.
- List what will run at the same time. Not everything you own. Only what must be on together in an outage.
- Add up the running watts. Use each appliance’s nameplate, or the chart below.
- Add the largest extra starting load once. Find the appliance with the biggest gap between its starting and running watts, and add that gap.
- Add 20% in reserve. Multiply the running total by 1.2.
That gives you two numbers: the running watts you need and the starting watts you need. A generator must meet both.
Why only one starting load? Motors rarely start in the same instant, and you can make sure they do not by switching things on one at a time.
Our original guide to what size generator you need explains the method in more depth, and our Generator Size Calculator does the arithmetic for you.
The 2026 Wattage Chart
| Appliance | Running watts | Starting watts | Voltage |
|---|---|---|---|
| Refrigerator or freezer | 700 | 2,200 | 120 |
| Sump pump, 1/3 hp | 800 | 1,300 | 120 |
| Gas furnace blower, 1/2 hp | 800 | 2,350 | 120 |
| Well pump, 1/2 hp | 1,000 | 2,100 | 240 |
| Lights, several rooms | 300 | 300 | 120 |
| TV, router and chargers | 300 | 300 | 120 |
| Microwave oven | 1,500 | 1,500 | 120 |
| Window air conditioner, 10,000 BTU | 1,200 | 3,600 | 120 |
| Central air conditioner, 24,000 BTU | 3,800 | 11,400 | 240 |
| Electric water heater | 4,500 | 4,500 | 240 |
| Electric range, one element | 2,100 | 2,100 | 240 |
| Electric clothes dryer | 5,400 | 6,750 | 240 |
These are deliberately cautious figures. A modern refrigerator often draws far less than 700 watts. The chart protects you from buying too small. Measuring your own appliances protects you from buying too big.
The newer loads
These are the loads that have changed sizing in recent years.
| Load | Typical draw | What to do in an outage |
|---|---|---|
| EV charging, Level 1, 12 amps at 120 volts | About 1,400 watts | Possible on a mid-size generator, but slow |
| EV charging, Level 2, 32 amps at 240 volts | About 7,700 watts | Leave it off, or turn the charge rate right down |
| EV charging, Level 2, 48 amps at 240 volts | About 11,500 watts | Leave it off. This alone is half a 22 kW generator |
| Heat pump or mini-split | Varies widely. Read the nameplate | Size for it if it is your only heat |
| Electric tankless water heater | Very high. Often several times a tank heater | Do not plan to run it on a home generator |
| Induction or electric range | About 2,100 watts per element | Use one element at a time, or a microwave |
| Home office and networking | A few hundred watts | Easy. Use clean inverter power or a battery backup |
Two points stand out. First, an electric vehicle charger is the largest single load in many homes. Charging at full speed during an outage makes no sense on any home generator. Many chargers and vehicles let you lower the charge rate, and that is the setting to use. Second, a heat pump that is your only source of heat belongs on the must-have list in a cold climate, and it has to be sized from its own nameplate.
The 2026 Sizing Chart by Home Type
Here is the summary. The six worked examples that follow show where each row comes from.
| Home | What runs | Running watts needed, with reserve | Starting watts needed | Generator to look for |
|---|---|---|---|---|
| Apartment or condo | Refrigerator, lights, electronics | About 1,600 | 2,800 | A 1,500-watt power station with a 3,000-watt surge, or a 3,000-watt inverter |
| Small house, gas heat | Add a furnace blower | About 2,500 | 3,650 | A 3,000 to 3,600-watt generator |
| House with a sump pump and freezer | Add a sump pump and a freezer | About 4,300 | 5,150 | A 4,500 to 5,500-watt generator |
| Rural home on a well | Add a well pump and a microwave | About 7,300 | 7,650 | A 7,500 to 9,500-watt generator with a 240-volt outlet |
| Whole home with central air | Add a central air conditioner | About 11,900 | 17,500 | A 14 to 22 kW standby generator |
| All-electric home with an EV | Add electric water heating, cooking and a dryer | 20,000 or more | Depends on load management | A 22 to 28 kW standby generator with load management |
Six Worked Examples
Example 1: an apartment
Loads: a refrigerator at 700 watts, lights at 300 and electronics at 300.
Running total: 1,300 watts. Largest start: the refrigerator needs 2,200 watts to start, which is 1,500 above its running figure. Starting demand: 2,800 watts. With reserve: about 1,600 running watts.
What fits: an apartment usually has no safe place to run an engine. A battery power station with 1,500 watts of output and a 3,000-watt surge covers this. If you have a safe outdoor spot, a 3,000-watt inverter generator does too.
Example 2: a small house with gas heat
Loads: refrigerator 700, furnace blower 800, lights 300, electronics 300.
Running total: 2,100 watts. Largest start: the furnace blower, which adds 1,550. Starting demand: 3,650 watts. With reserve: about 2,500 running watts.
What fits: a generator with 3,000 to 3,600 running watts and about 4,000 starting watts. A mid-size inverter is ideal here, because it is quiet and makes clean power for the furnace’s control board.
Example 3: a house with a sump pump and a freezer
Loads: Example 2, plus a sump pump at 800 and a chest freezer at 700.
Running total: 3,600 watts. Largest start: still the furnace blower, at 1,550. Starting demand: 5,150 watts. With reserve: about 4,300 running watts.
What fits: a generator with 4,500 to 5,500 running watts. This is the classic open-frame portable, and it is where most first-time buyers land.
Example 4: a rural home on a well
Loads: Example 3, plus a 1/2 hp well pump at 1,000 and a microwave at 1,500.
Running total: 6,100 watts. Largest start: the furnace blower, at 1,550. Starting demand: 7,650 watts. With reserve: about 7,300 running watts.
What fits: a generator with 7,500 to 9,500 running watts. It must have a 240-volt outlet, because the well pump needs it, and it should be connected through a transfer switch. You cannot run a hard-wired well pump from an extension cord.
Example 5: a whole home with central air
Loads: Example 4, plus a 24,000 BTU central air conditioner at 3,800 watts.
Running total: 9,900 watts. Largest start: the air conditioner, which adds 7,600. Starting demand: 17,500 watts. With reserve: about 11,900 running watts.
What fits: this is beyond ordinary portables. A 14 kW standby generator covers the running load with a little to spare. An 18 to 22 kW unit gives real comfort. Standby generators are built to handle motor starting, and a soft-start kit on the air conditioner makes the job much easier.
Example 6: an all-electric home with an EV
Loads: Example 5, plus an electric water heater at 4,500, a range element at 2,100 and a dryer at 5,400. The EV charger is left off.
Running total if everything ran at once: 21,900 watts. In real life it never all runs at once.
What fits: a 22 to 28 kW standby generator with load management. A load manager holds back the water heater, the dryer and the range so they take turns. Without it, you would need a much larger and more costly generator. The EV charger should be locked out during an outage, or set to a very low charge rate.
Key insight: from Example 1 to Example 4, each added appliance moves you up one size of portable. The jump to Example 5 is different. Central air changes the kind of generator you need, not just its size.
Two Tools That Shrink the Generator You Need
Soft starters
The starting surge of an air conditioner is what pushes many homes into a bigger generator. A soft starter is a small electronic device wired into the air conditioner. It brings the compressor up to speed gradually, instead of all at once.
The maker of one well-known product line says its soft starter lowers the compressor’s inrush current by up to 75%. That is the maker’s claim, and results vary with the air conditioner. Even a smaller reduction can let a 14 kW generator do what would otherwise need 20 kW, or let a small inverter run an RV air conditioner.
Fitting a soft starter to a home system means working inside the outdoor unit. Have an HVAC technician do it, and check that it does not affect your warranty.
Load management
A standby generator’s transfer switch can be fitted with load management modules. These watch how hard the generator is working. When it is near its limit, they hold back lower-priority appliances and let them run later.
Generac calls its version the Load Manager. Kohler and Champion offer their own. The effect is the same: a smaller generator can serve a larger home. It is cheaper to buy and cheaper to fuel.
Tip: decide what can wait
Load management works because many big appliances can wait ten minutes without anyone noticing. A water heater, a dryer and an EV charger are all patient. A sump pump, a refrigerator and medical equipment are not. Put the patient loads on managed circuits and size the generator for the rest.
Three Things That Cut a Generator’s Real Output
The number on the box assumes gasoline, sea level and mild weather. Your conditions may be different.
| Factor | Typical effect | Source |
|---|---|---|
| Propane on a dual fuel portable | About 10% less than gasoline | Makers’ ratings |
| Natural gas on a tri fuel portable | About 20% or more less than gasoline | Makers’ ratings |
| Natural gas on a standby generator | A few percent to about 14% less than propane | Generac and Kohler ratings |
| Altitude, portable generator | About 3.5% less per 1,000 feet | Champion owner’s manual |
| Altitude, air-cooled standby generator | About 4% less per 1,000 feet above 500 feet | Kohler spec sheets |
| Heat, air-cooled standby generator | About 2% less per 10°F above 60°F | Kohler spec sheets |
A derating example
Take Example 4, which needs 7,300 running watts. Suppose you live at 5,000 feet and plan to run on propane.
- Start with the need: 7,300 running watts.
- Allow for altitude. At 5,000 feet, a portable loses about 17.5%. It delivers about 82.5% of its rating.
- Allow for propane. It delivers about 90% of what remains.
- Combine them. 0.825 multiplied by 0.90 is about 0.74.
- Divide. 7,300 divided by 0.74 is about 9,900.
So at 5,000 feet on propane, you need a generator rated at about 9,900 running watts on gasoline at sea level to get 7,300 where you live. That is a full size class larger. Ignore derating, and the generator you bought on paper will not carry your house.
Voltage and Outlets: The Check People Skip
Watts are not the whole story. Two more checks matter.
Do you need 240 volts? A well pump, central air, an electric water heater, a range and a dryer all run on 240 volts. Many inverter generators and small portables are 120 volts only. No amount of wattage helps if the voltage is wrong.
Can the outlet pass the power? A 30-amp, 240-volt outlet passes 7,200 watts at most. A 50-amp outlet passes 12,000. A generator rated above its largest outlet cannot send all its power to your transfer switch.
Size it right, then connect it right
Run a portable generator outdoors only, at least 20 feet from the house, with the exhaust pointing away from doors, windows and vents. Never plug a generator into a wall outlet. To power house circuits, have a licensed electrician fit a transfer switch or an interlock. Fit carbon monoxide alarms on every level of your home. A standby generator must be installed by licensed trades, to the maker’s clearances and your local code.
Our guide on how to connect a generator to your house explains the options.
Measure Instead of Guessing
Charts are cautious on purpose. Real appliances often use much less. Three ways to get real numbers:
- Read the nameplate. It lists watts, or amps and volts. Multiply amps by volts to get watts.
- Use a plug-in power meter on 120-volt appliances. It shows the running watts directly.
- Look for LRA on an air conditioner or heat pump. LRA means locked rotor amps. It is the current the compressor draws for an instant as it starts. Multiply it by the voltage for a rough idea of the starting load. An HVAC technician can read it for you.
Measuring can move you down a size, which saves money on the generator and on every gallon of fuel it burns.
One Generator for Each Example
We have not tested these products. Details come from makers’ pages and Amazon listings, and stock changes quickly.
Start by measuring
P3 P4400 Kill A Watt Electricity Usage Monitor
A plug-in meter that shows the watts a 120-volt appliance really uses. It replaces chart values with your own numbers.
- DisplaysVolts, amps, watts, kilowatt-hours
- Accuracy on listingWithin 0.2 to 2.0%
- For115-volt AC appliances
- Capacity15 amps
- DisplayLCD
- Warranty1 year limited
- Why it works: real running watts are often lower than chart figures, so you can size more accurately.
- Who it is best for: anyone choosing between two generator sizes.
- What it solves: overbuying, and the fuel cost that comes with it.
- Keep in mind: it reads steady running watts, not the split-second starting surge. It works on 120-volt plug-in appliances only.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Example 2: small house
Champion 4500-Watt Electric Start Dual Fuel Portable Inverter Generator
A quiet inverter with 3,500 running watts on gasoline and 3,150 on propane. It covers the small house example with clean power.
- Starting watts4,500 W
- Running watts3,500 W gasoline, 3,150 W propane
- Noise level61 dBA
- Run time on gasolineUp to 14 hours
- Run time on propaneUp to 21 hours
- Weight99.2 lb
- Why it works: Example 2 needs 2,500 running and 3,650 starting watts. This has both, on either fuel.
- Who it is best for: small homes with gas heat and city water.
- What it solves: a refrigerator, a furnace blower, lights and electronics, quietly.
- Keep in mind: it is 120 volts only, so it cannot run a well pump. By Champion’s naming, 4,500 is the starting figure.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Example 3: sump pump and freezer
Generac GP5500E Portable Generator with EFI and Electric Start (6,875 Starting Watts)
A mid-size open-frame generator with fuel injection. It makes 5,500 running watts and 6,875 starting watts.
- Running / starting watts5,500 / 6,875
- Engine298 cc OHV with EFI
- StartElectric, battery included
- Run timeUp to 11 hours at 50% load
- SafetyCOsense shutdown, low-oil shutdown
- Weight163 lb on the listing
- Why it works: Example 3 needs 4,300 running and 5,150 starting watts. This covers it with margin.
- Who it is best for: homes with a sump pump, a freezer and a gas furnace.
- What it solves: essentials for a day or two, with easier starting after storage.
- Keep in mind: it is loud, like any open-frame generator. Shipping took a few days when we checked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Generac’s product page and the Amazon listing, checked October 2026.
Example 4: home on a well
Westinghouse WGen9500DFc Dual Fuel Portable Generator with CO Sensor (12,500 Peak Watts)
A large dual fuel generator with 9,500 running watts on gasoline and 8,500 on propane, and both 30-amp and 50-amp 240-volt outlets.
- Running watts9,500 gasoline, 8,500 propane
- Peak watts12,500 gasoline, 11,200 propane
- Engine457 cc OHV
- Fuel tank6.6 gallons
- Run timeUp to 12 hours
- Warranty on listing3-year limited
- Why it works: Example 4 needs 7,300 running and 7,650 starting watts at 240 volts. This covers it on either fuel.
- Who it is best for: rural homes with a well pump, connected through a transfer switch.
- What it solves: water, heat, cold food and cooking in a long outage.
- Keep in mind: it weighs about 212 pounds. At altitude and on propane, its output falls, as the derating example shows.
As an Amazon Associate we earn from qualifying purchases. Specs come from the Amazon listing, checked October 2026.
Example 5: whole home
Generac 22 kW Whole Home Generator with Transfer Switch and Cellular Monitoring
An automatic standby generator rated at 22 kW on propane and 21 kW on natural gas, sold with a transfer switch.
- Rating22 kW on LP, 21 kW on NG
- Amps at 240 VAbout 92
- EngineGenerac G-Force 1000
- Natural gas at half load221 cubic feet per hour
- Weight451 lb
- Warranty on listing5-year limited
- Why it works: Example 5 needs about 11,900 running watts with a large starting surge. This has nearly double that.
- Who it is best for: family homes with central air, and all-electric homes with load management.
- What it solves: the jump from essentials to normal life in an outage.
- Keep in mind: installation, permits and gas work are a separate cost. Have a dealer do a load assessment first. Stock was limited when we checked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Generac’s product pages and the Amazon listing, checked October 2026.
Shrink the surge
Micro-Air EasyStart Breeze 399 Bluetooth Soft Start for RV Air Conditioners
A soft starter for RV rooftop air conditioners. The listing says it suits most units up to 18,000 BTU and lets an air conditioner run from a single 2,200-watt inverter generator.
- ForRV rooftop air conditioners up to 18,000 BTU
- Install on listingUnder 30 minutes
- Harness40 inches, color-coded
- MonitoringBluetooth
- Maker’s claimRuns an RV AC on a 2,200 W inverter
- Stock on listingIn stock when checked
- Why it works: it cuts the compressor’s starting surge, which is the reason small generators fail to start an air conditioner.
- Who it is best for: RV owners with a small inverter generator.
- What it solves: buying a second generator or a parallel kit just to start the air conditioner.
- Keep in mind: this model is for RV air conditioners. Micro-Air sells a separate version for home systems, which should be fitted by an HVAC technician. The performance figure is the maker’s claim.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Portable or Standby: Where the Line Falls in 2026
| Your result | Likely choice | Why |
|---|---|---|
| Under 3,000 running watts | Inverter generator or battery power station | Quiet, light and enough |
| 3,000 to 9,500 running watts | Portable generator, with a transfer switch at the upper end | The best value for essentials |
| Central air on the list | Standby generator, 14 kW or more | The starting surge is beyond most portables |
| All-electric home | Standby generator with load management | Too many 240-volt loads for a portable |
| House often empty | Standby generator | A portable needs someone at home |
Our guides to portable vs standby generators and whole-house generators go deeper.
Common Generator Sizing Mistakes (and the Fix)
Pro Tips for Sizing in 2026
- Start with the must-haves. A sump pump or medical device sets the floor.
- Think seasonally. Your summer list and your winter list are different. Size for the bigger one.
- Stagger big loads. Start the largest motor first, then add the rest one by one.
- Plan for the house you will have. A heat pump, a well or an EV in the next few years belongs on the list now.
- Ask your utility or electrician about your peak demand. Some electric bills and smart meters show it.
- Do not oversize by a wide margin. A generator far bigger than its load wastes fuel.
- Get a load assessment before you buy a standby generator.
Real-Life Scenarios: What Size Would You Pick?
These are typical situations. They are examples to help you decide, not reports from real customers.
🏔️ The mountain cabin
7,000 feet up, propane only, with a well pump, a refrigerator and lights.
Altitude takes about a quarter of the rating, and propane another tenth. Buy about half as much again as the sums suggest.
Size: step up one or two classes
🚗 The EV household
A 48-amp charger, central air and a gas furnace.
Size for the house, not the car. Lock the charger out during outages and consider load management.
Size: 18 to 22 kW standby
🌡️ The heat pump home
A heat pump is the only heat, in a cold climate.
The heat pump is a must-have. Read its nameplate, ask about a soft starter, and get a dealer assessment.
Size: standby, by assessment
What Size Generator Do I Need: FAQ
What size generator do I need to run my whole house?
For a typical home with central air, a 14 to 22 kW standby generator. Smaller homes can use the lower end, especially with a soft starter or load management. All-electric homes usually need 22 kW or more with load management. A dealer's load assessment gives the exact size.
What size generator do I need for just the essentials?
Most homes need 3,500 to 7,500 running watts for a refrigerator, a furnace blower, lights, electronics and a sump or well pump. A home on a well needs a generator with a 240-volt outlet.
How do I calculate what size generator I need?
Add the running watts of everything that must run together. Add the extra starting watts of the largest motor once. Multiply the running total by 1.2 for reserve. Then adjust for your fuel and altitude.
Can a generator charge an electric car?
Slowly, yes. Level 1 charging at 12 amps draws about 1,400 watts, which a mid-size generator can supply. Level 2 charging draws 7,700 to 11,500 watts, which is too much to add to a home's other loads. Lower the charge rate or wait for the grid.
Does altitude affect generator size?
Yes. Champion's manual gives about 3.5% less output per 1,000 feet for a portable. Kohler's spec sheets give about 4% per 1,000 feet above 500 feet for its air-cooled standby units. At 5,000 feet, plan on a generator about 20% larger.
Will a soft starter let me use a smaller generator?
Often, yes. A soft starter reduces the starting surge of an air conditioner, which is usually what forces a larger generator. One maker claims a reduction of up to 75%. Results vary, so have an HVAC technician advise on your unit.
Your 2026 Generator Sizing Checklist
- List what must run at the same time.
- Note which loads need 240 volts.
- Add the running watts.
- Add the largest extra starting load once.
- Multiply the running total by 1.2.
- Derate for your fuel.
- Derate for your altitude.
- Leave EV charging out, or plan a low rate.
- Consider a soft starter and load management.
- Check the generator’s largest outlet can pass the power you need.
- Measure real appliances where you can.
- Get a load assessment for a standby generator.
The bottom line
The method is the same as ever: running watts, the biggest start and 20% in reserve. What is new in 2026 is the list of loads and the tools for managing them. Leave the EV charger off, soften the air conditioner’s start, derate for your fuel and altitude, and the right size becomes clear.
As an Amazon Associate we earn from qualifying purchases.
Sources: Typical appliance wattages in line with commonly published charts, as used in our generator sizing guide; Champion Power Equipment’s owner’s manual for derating on portables; Kohler specification sheets for derating on air-cooled standby generators; Generac’s, Kohler’s and Champion’s published fuel ratings and load management information; Generac’s EV charger specifications; Amazon listings for the products named in this guide. All checked October 2026.
