The most common generator buying mistake is picking a number out of thin air — "I'll get a 5,000-watt one" — and either overspending on capacity you don't need or buying something underpowered that trips under real load. The right size comes from one simple process: add up what you actually want to run, then add a safety buffer. Here's exactly how to do it.

The Short Answer

⚡
For most homes during a typical outage: A 3,500–5,000W generator covers refrigerator, lights, fans, TV, phone/laptop charging, and a window AC. If you want to run central HVAC, you'll need 7,500–10,000W+. For a solar battery station covering essentials (no central AC), 1,000–2,000Wh capacity with 1,500–2,000W output is usually enough.

Wattage Calculator

Check the appliances you want to power during an outage. We'll calculate your minimum generator size.

Common Appliance Wattage Reference

Understanding the difference between running watts (what an appliance uses continuously) and starting watts (the surge it needs to start its motor) is critical for sizing correctly.

Appliance Running Watts Starting Watts Notes
Refrigerator (full-size)150W800WCycles on/off; avg ~40–60Wh/hr
Window AC (5,000 BTU)500W1,500WStarting surge is brief — a few seconds
Window AC (10,000 BTU)900W2,200WPopular room AC size
Central AC (3-ton)3,500W7,500WRequires 7,500W+ generator
Sump pump (1/2 HP)800W2,150WCritical during flooding events
Well pump (1/2 HP)900W2,100WEssential for homes on well water
Furnace fan800W2,350WMost gas furnaces need 600–800W to run fan
Microwave (1,000W)1,000W1,000WNo motor — no starting surge
Electric range / oven3,000–5,000WSameUsually impractical for generator use
Electric dryer5,400W6,750WHigh draw — skip during outages
TV (55" LED)100W100WVery low draw
Laptop45–65WSameUse USB-C PD charging
LED lights (per bulb)8–12WSame10 bulbs ≈ 100W total
CPAP (no heated hum.)30–60WSameMost solar generators handle this easily
Router + modem15–25WSameKeep internet running during outages

How to Size a Generator: Step by Step

Step 1: Decide what you absolutely must power

Be honest about your actual priorities. Most people need: refrigerator, lights, phone and laptop charging, router, and a fan or window AC. Write that list down. Central AC and electric ranges are usually luxuries during a short outage — plan to do without.

Step 2: Add up the running watts

Look up or measure the running wattage of each appliance you plan to run simultaneously. Add them together. This is your baseline load.

Step 3: Find your highest starting surge

Motor-driven appliances (compressors, pumps, AC units) require a surge of 2–3× their running watts to start. You need to add the single highest starting wattage to your running total — this is the peak demand your generator will see when the motor kicks on.

Step 4: Add 20% headroom

Running a generator at 80–90% capacity continuously shortens its life and can cause voltage instability. Add 20% to your peak demand calculation. This is your minimum recommended generator size.

Practical example

📋
Scenario: Weekend outage, essential backup
Refrigerator: 150W | Window AC: 500W | TV: 100W | Router: 20W | Lights: 100W | Phone/laptop: 80W
Running total: 950W
Highest starting surge (window AC): +1,500W
Peak demand: 2,450W
Add 20% headroom: Minimum generator size: 2,940W → buy a 3,500W unit

Recommended Products by Size

Under 2,000W — Solar Battery Station

If your essential loads total under 1,500W, a solar battery generator is the smarter choice. Silent, no fuel needed, safe indoors, and recharges from sun or wall. Our top picks:

3,500–5,500W — Mid-Size Gas or Dual Fuel

Handles most households without central AC. These cover the sweet spot of capability vs cost for most homeowners.

7,500–10,000W — Large Home Backup

Handles central AC, well pumps, sump pumps, and everything else simultaneously.

Frequently Asked Questions

What generator size do I need for a 2,000 sq ft house?
Square footage is misleading for generator sizing — what matters is which appliances you run, not the floor plan. A 2,000 sq ft home with central AC needs 7,500–10,000W. Without central AC (window units instead), 3,500–5,000W covers most needs. Use the calculator above for a personalized answer.
Can I run my well pump on a generator?
Yes, but size it carefully. A 1/2 HP well pump draws 900W running and 2,100W starting. Make sure your generator's surge/peak capacity covers the starting watts. A 3,500W generator can technically start it, but you'd want 4,000W+ for comfortable headroom if running other loads simultaneously.
What's the difference between running watts and peak watts?
Running watts (also called "rated watts") is the continuous power a generator produces — what it can sustain indefinitely. Peak watts (also called "starting watts" or "surge watts") is the higher wattage it can produce briefly (typically 10–30 seconds) to start motor-driven appliances. Always size based on running watts for your continuous load, and check that peak watts covers your largest motor's startup surge.
Do I need a transfer switch to use a generator?
For portable generators powering individual appliances via extension cords: no. For connecting to your home's electrical panel (so outlets in your house work normally): yes, you need a transfer switch — and it must be installed by a licensed electrician. Running a generator through your panel without a transfer switch is dangerous and illegal. Learn more about transfer switches →
How loud is a generator?
Conventional gas generators run 65–75 dB at 23 feet — roughly as loud as a vacuum cleaner. Inverter generators are significantly quieter at 52–58 dB. Solar battery generators make no engine noise at all (only a light fan hum). If noise is a concern for you or your neighbors, an inverter generator or solar battery station is worth the premium.