Power outages are lasting longer and happening more frequently. When the grid fails, will you have enough backup power to keep your family safe, fed, and comfortable?
This Calculator Tells You Exactly What Size Generator You Need For:
Generator Sizing Calculator
Select the appliances you want to power and we’ll calculate exactly what size generator you need
Essential Appliances
Heating & Cooling
Kitchen Appliances
Medical Equipment
Power Tools
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Your Power Requirements
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Power Outages Are Getting Worse
According to JD Power’s November 2025 survey, 45% of utility customers nationwide experienced a power outage in the first half of 2025. More concerning: the average outage duration increased from 8.1 hours in 2022 to 12.8 hours by mid-2025—a 58% increase in just three years.
Research from Texas A&M University shows outages have gotten 20% worse each year since 2019, lasting longer, happening more frequently, and affecting more people. Weather causes 83% of all outages, and extreme weather events doubled in the last decade compared to the first decade of the 2000s.
When power went out in Springfield, Missouri in April 2025, officials warned residents to prepare for multi-day outages comparable to the devastating ice storms of 2007-2008. In Charlotte, slow-moving storms left thousands without power for days. These aren’t isolated incidents—they’re the new normal.
The good news? With the right-sized generator, you don’t have to sit in the dark waiting for the grid to come back. Calculate your needs above, then invest in reliable backup power before the next storm hits.
How to Choose the Right Generator Size
Buying a generator without calculating your wattage needs is like buying shoes without knowing your size. Too small and it won’t run your essentials. Too large and you’re wasting money on capacity you’ll never use.
The key is understanding two numbers: running watts (continuous power during normal operation) and starting watts (surge power needed when motors kick on). Your generator must handle the sum of all running watts PLUS the highest individual starting surge. That’s what our calculator does—it accounts for both to give you an accurate recommendation.
Most families need 3,000-7,000 watts for essentials (refrigerator, lights, furnace, some outlets). If you want central AC, you’re looking at 12,000-15,000 watts. For whole-house coverage including electric water heater and range, expect 15,000-20,000 watts.
Why Batten Emergency
We research backup power solutions using real-world testing and industry data—not marketing claims. Every generator we recommend has been evaluated for reliability, fuel efficiency, and actual power output under load.
Whether you need a portable generator for occasional outages or a whole-house system for complete peace of mind, we provide honest recommendations based on your actual needs. Your family’s safety during emergencies deserves that level of scrutiny.
Generator Sizing Questions
What’s the difference between running watts and starting watts?
Running watts (also called rated watts) is the continuous power an appliance uses during normal operation. Starting watts (or surge watts) is the extra power needed when an appliance first turns on. Motor-driven appliances like refrigerators, air conditioners, and sump pumps require 2-3 times their running watts to start. Your generator must handle both the total running watts of all connected appliances AND the highest starting watts surge.
Should I buy a portable or whole-house generator?
Portable generators (typically 2-10 kW) are best if you want to power essential items like refrigerators, lights, and a few outlets during outages. They’re more affordable ($400-$2,000) and you can move them as needed. Whole-house generators (10-25 kW) are permanently installed, automatically turn on during outages, and can power your entire home including central AC and heating. They cost $3,000-$15,000+ including installation but provide seamless backup power.
How much power does my refrigerator need?
A standard refrigerator uses 600-800 running watts but requires 1,800-2,400 starting watts when the compressor kicks on. Larger side-by-side models can need up to 2,000 starting watts. Always check your refrigerator’s nameplate or manual for exact specifications, as energy-efficient models may use less power.
Can I run my whole house on a portable generator?
Most homes cannot run everything simultaneously on a portable generator. A typical home needs 15,000-20,000 watts to power all circuits. However, you can run essential items (refrigerator, lights, furnace fan, some outlets) on a 7,000-10,000 watt portable generator with load management—avoiding running high-draw appliances like AC, electric water heater, and electric stove at the same time.
How do I prevent overloading my generator?
Never exceed your generator’s rated wattage capacity. Calculate your total running watts, add the highest starting watts surge, and keep the total below 80% of your generator’s maximum output for safety. Use load management by starting motor-driven appliances one at a time, turning off non-essential items, and avoiding simultaneous use of high-wattage appliances like AC and electric dryers.
What size generator do I need for power tools?
Construction power tools vary widely in wattage. A circular saw needs 1,400-2,000 watts, table saw 1,800-2,500 watts, and air compressor 1,500-4,500 watts depending on size. For job sites, a 7,000-8,000 watt generator handles most tool combinations. For heavy equipment like welders or large compressors, you may need 10,000+ watts.
Do I need a transfer switch for my generator?
A transfer switch is strongly recommended for home use. It safely connects your generator to your home’s electrical panel, prevents dangerous backfeed to utility lines, and allows you to power hardwired appliances like furnaces and well pumps. Manual transfer switches cost $300-$800 installed. Automatic transfer switches for whole-house generators cost $1,500-$3,000 but provide seamless power switching.
How long can I run a generator continuously?
Most portable generators can run 8-12 hours continuously on a full tank of gas at 50% load. Larger generators with bigger fuel tanks can run 12-24 hours. For extended outages, you’ll need to shut down periodically to refuel and perform maintenance like checking oil. Whole-house generators connected to natural gas or large propane tanks can run for days or weeks with only routine maintenance checks.