Generator Sizing Guide: What Watts?

The number one question people ask before buying a generator is "how many watts do I need?" The answer depends on what you want to power. This guide gives you the exact wattage figures for common household appliances, walks you through the calculation process, and matches you with the right generator for your needs.

Understanding Watts: Running vs. Starting

Every appliance has two wattage numbers that matter:

Running watts (also called rated watts) is the continuous power the appliance draws during normal operation. A refrigerator might run at 150 watts.

Starting watts (also called surge or peak watts) is the brief power spike when a motor-driven appliance starts up. That same refrigerator might surge to 1200 watts for 1-3 seconds when the compressor kicks on.

Your generator needs enough running watts for everything you plan to operate simultaneously, and enough starting watts to handle the highest individual motor startup on top of the running load.

Common Appliance Wattage Chart

How to Calculate Your Needs

Follow these three steps:

Step 1: List Your Essential Appliances

Write down everything you want to power during an outage. Be realistic. You probably do not need the microwave and coffee maker running simultaneously with the AC unit. Prioritize by category:

• Must have: Refrigerator, lights, phone charging, medical devices
• Important: Fans or AC, sump pump (if flooding risk), Wi-Fi router
• Nice to have: TV, microwave, coffee maker

Step 2: Add Up Running Watts

Total the running watts of everything you want to operate simultaneously. Example for a basic essentials setup:

Step 3: Identify the Highest Starting Load

Find the appliance with the highest starting wattage. In this example, the refrigerator surges to 1200W when its compressor kicks on. Add this surge to the running total of everything else:

390 (total running) - 150 (fridge running, since it is surging) + 1200 (fridge starting) = 1440 starting watts needed

So you need a generator with at least 390 running watts and 1440 starting watts. A Champion 2000W inverter generator (1700 running / 2000 starting) handles this with room to spare.

Scenario Calculations

Scenario 1: Basic Essentials (2000W)

Refrigerator + lights + phones + fan + router

Running: ~400W | Starting: ~1400W

Recommended: Champion 2000W (~$450) or WEN 56203i (~$400)

Scenario 2: Essentials + Window AC (3500W)

Everything in Scenario 1 + 5000 BTU window AC

Running: ~900W | Starting: ~2200W (AC compressor on top of running load)

Recommended: Champion 4500W Dual Fuel (~$650)

Scenario 3: Essentials + AC + Sump Pump (4500W)

Everything in Scenario 2 + 1/3 HP sump pump

Running: ~1700W | Starting: ~3500W (sump pump on top of everything)

Recommended: Westinghouse iGen4500 (~$900) or DuroMax XP5500EH (~$550)

Scenario 4: Maximum Portable Coverage (7000W+)

Refrigerator + freezer + AC + sump pump + well pump + lights + electronics

Running: ~3500W | Starting: ~6000W

Recommended: Two Honda EU2200i units in parallel (~$2,300) or a large conventional generator

The 80% Rule

Never run a generator at more than 80% of its rated capacity for extended periods. Running at full load increases fuel consumption, accelerates engine wear, and reduces lifespan. If your calculations show you need 2800 running watts, buy a generator rated for at least 3500 running watts (2800 / 0.80 = 3500).

This buffer also protects against load spikes you did not anticipate: a second appliance's compressor kicking on while the first is running, a power tool briefly plugged in for storm cleanup, etc.

Generator Recommendations by Power Level

Transfer Switch: The Safe Way to Power Your Home

A transfer switch is an electrical panel installed by a licensed electrician that lets you safely connect a portable generator to your home's wiring. It prevents backfeed (sending power back into utility lines, which can electrocute lineworkers) and lets you power hard-wired circuits like the well pump, sump pump, and overhead lights.

Without a transfer switch, you are limited to running extension cords from the generator to individual appliances. With a transfer switch, you flip breakers to select which circuits receive generator power.

A basic Reliance Controls 6-circuit transfer switch costs about $150-200 for the panel, plus $200-400 for professional installation. It is a worthwhile investment if you plan to use a generator regularly.

Power Station as a Complement

Consider pairing your generator with a portable power station for the best of both worlds. Use the power station for silent, indoor-safe operation of electronics (phones, laptops, CPAP, router) and the generator for heavy loads (refrigerator, AC, sump pump) when needed. This lets you run the generator less frequently, saving fuel and reducing noise exposure.

Read our full generator guide and power station guide for detailed product reviews.

Common Sizing Mistakes

• Ignoring starting watts: A generator with 2000 running watts cannot start a window AC unit that surges to 1500W on top of existing loads.
• Planning to run everything at once: Stagger loads instead. Run the refrigerator for 4 hours, turn it off, then run the AC for 2 hours. Alternating extends fuel supply dramatically.
• Buying too small: A generator at 100% load burns fuel faster, runs hotter, and dies sooner than one at 50-70% load. Size up.
• Forgetting the sump pump: If your basement floods during storms, the sump pump is the most critical load. Its high starting wattage often determines the minimum generator size.

Final Recommendation

For most households, a Champion 4500W Dual Fuel inverter generator at about $650 is the sweet spot. It handles a refrigerator, window AC, lights, electronics, and a sump pump simultaneously. The dual-fuel capability provides fuel flexibility, and the inverter technology produces clean power for all your electronics. It is the generator we recommend most often for storm preparedness.