What Size Generator Do I Need?
Most homes typically require a 5000–12,500-watt generator to keep essential appliances running during an outage.
Wondering, “what size generator do I need?” Selecting the appropriate generator size is key to keeping your essentials running smoothly, whether you’re facing a home power outage, powering tools at a job site, or enjoying the great outdoors.
With so many options available, determining what size generator to run a house can feel overwhelming. This guide is here to assist you in understanding what size generator you need for your house, exploring different generator types, and utilizing sizing tools to make a solid choice.
Types of Generators
When figuring out “what size generator do I need” for my house, it helps to know the different types. Portable generators are convenient for everything from camping trips to home backup during outages. They’re generally smaller and easy to move, making them a preferred choice for temporary power needs. In contrast, home standby generators are installed permanently and activate automatically during outages, providing whole-house backup.
- Portable Generators:
- Standard units that provide electrical power for devices, tools, appliances, or recreation. Available in ranges from 1000–22,000+ watts, they are economical, durable, powerful, and portable.
- Inverter Generators:
- Quieter and lighter than standard portable generators, inverters produce clean, stable power ideal for sensitive electronics like phones and laptops. Larger inverter generators can also support electric vehicle charging. Typically ranging from 1000–11,000+ watts, they use intelligent microprocessors to adjust engine speed based on load — improving fuel efficiency and extending engine life.
- Home Standby Generators: permanent whole house generators ranging from 8500–26,000+ watts that automatically restore power within seconds of an outage being detected. Professional installation required.
⚠️ Safety Note — Home Backup Use
When using a portable generator for home backup power, it must be connected to a manual transfer switch installed by a licensed electrician. This ensures safe operation and proper distribution of power to your selected circuits.
- The generator must always be operated outside to avoid the dangers of carbon monoxide.
Fuel Types
Your generator’s fuel type also influences its size and capacity. They can operate on gasoline, propane, or natural gas.
- Dual Fuel Generators and Inverters: operational using either gasoline or propane.
- Tri Fuel Generators and Inverters: capable of running on gasoline, propane, or natural gas.
Gasoline
- Fuel readily available around the world
- No additional fuel tank is needed for run time
- Provides highest power output
Propane
- Costs less than gasoline
- Clean burning fuel with a longer shelf life
- No fuel degradation during storage
- Note: propane typically delivers approximately 10% less wattage output than gasoline — factor this in when sizing
Natural Gas
- Lowest cost of the three options
- No refills needed — connects directly to your home’s utility line
- Note: natural gas typically delivers approximately 10–15% less wattage output than gasoline — factor this in when sizing
Calculating Your Power Needs
To determine the right size for your power needs, start with the wattage requirements of your key appliances. Each appliance usually has a wattage label or it’s listed in the manual. Create a list of everything you want to power during an outage, from the fridge to your most critical appliances, and note their wattage needs. You can use our Wattage Reference Chart to help guide you on determining wattage of a tool or appliance.
What is Wattage?
Wattage refers to the amount of electrical power needed to run a device, tool, or appliance.
How to Calculate Wattage
Determining the wattage needed by a device, tool, or appliance is usually straightforward, but not always. While many products list wattage directly on their label, others may only provide volts and amps. In those cases, you’ll need a quick calculation to find the wattage.
Use the following formula when wattage isn’t listed:
- Volts (V) × Amps (A) = Watts (W)
Starting vs. Running Watts
Many appliances — like refrigerators and hair dryers — require both a starting wattage and a running wattage to operate properly. Simpler devices like light bulbs and laptops require only a running wattage. So keep in mind the difference between starting and running watts.
Starting watts: the additional burst of power certain devices require to start up. Starting watts are typically 1–2 times the running wattage and only last a fraction of a second.
Running watts: the continuous power a device needs to keep operating once it’s up and running. This is the number you’ll use for most of your calculations.
Determining Your Total Wattage Needs
Now that you understand how wattage works, follow these steps to estimate the generator size you’ll need:
- List all the appliances and devices you plan to power with a generator.
- Find the running watts for each item (use the label or calculate it if only volts and amps are listed).
- Add together all running watts to get your base power requirement.
- Identify the highest starting wattage among your appliances.
- Add that starting wattage to your total running watts to determine your peak power need.
This final number gives you a clear picture of the generator size required to keep everything running smoothly. With a wide range of options available, Champion Power Equipment makes it easy to find a generator that fits your specific home use power needs.
Wattage Reference Table
The appliances below represent the most common items people want to power. For a complete list of appliances, tools, and outdoor equipment, see our Generator Wattage Chart.
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Home & Backup Power | ||
| Refrigerator | 150–400W | 800–1200W |
| Freezer | 100–500W | 500–1000W |
| Window AC (10,000 BTU) | 900–1200W | 1800–2400W |
| Central AC (3 ton) | 3000–3500W | 5000–6000W |
| Furnace fan (1/2 HP) | 300–800W | 800–1600W |
| Sump pump (1/2 HP) | 800–1050W | 1300–2150W |
| Microwave | 600–1200W | —* |
| Space heater | 750–1500W | —* |
| TV | 80–400W | —* |
| LED lights (per bulb) | 8–15W | —* |
| Phone/laptop charger | 20–100W | —* |
| Job Site | ||
| Circular saw (7-1/4″) | 1200–1800W | 2400–3600W |
| Air compressor (2 HP) | 2500W | 7500W |
| Outdoors & Recreation | ||
| RV air conditioner (13,500 BTU) | 1500–2000W | 2800–3500W |
| RV refrigerator | 150–600W | 400–1000W |
— These appliances do not require extra starting watts. Size based on running watts only.
Understanding Generator Sizes
Generators come in various sizes for different tasks — here’s how to match your wattage needs to the right tier.
| Wattage | Typical Appliances | Best For |
|---|---|---|
| 1000–3000W | Lights, phone chargers, small appliances | Camping, tailgating, short outages |
| 3000–7000W | Refrigerator, freezer, window AC, TV | Home essentials during outages |
| 7000–12,500W | Central AC units, electric water heater, well pump, sump pump | Larger homes, job sites, extended outages |
| 12,500–22,000W | Whole-home coverage, multiple large appliances simultaneously like compressors and air conditioning | Whole-home portable backup, large job sites |
Recognizing these distinctions helps you determine what size works best for your power demands.
Need automatic whole-home generator backup? Home standby generators offer a permanent, automatic power system ranging from 8500–26,000 watts. Unlike portable generators, they activate within seconds of an outage — no setup required. What Size Generator Do I Need?
Frequently Asked Questions
What size generator do I need for a 2000 sq ft house? Most 2000 sq ft homes need a 5000–7500 watt generator to cover essentials like the refrigerator, lights, outlets, and a window AC unit. If you want to run central air conditioning, plan for 10,000 watts or more.
Will a 3500 watt generator run a refrigerator? Yes — a modern refrigerator typically runs at 150–400 watts and starts at around 800–1200 watts, well within a 3500W generator’s capacity. You’ll have remaining wattage for lights and small devices.
What’s the difference between starting watts and running watts? Running watts is the continuous power a device needs to operate. Starting watts is the brief power surge required to start appliances with motors — like refrigerators and air conditioners. Always size your generator to handle the highest starting wattage among your appliances, added to your total running wattage.
Do I need a transfer switch for a portable generator? Yes, if you’re connecting a portable generator to your home’s electrical system. A manual transfer switch, installed by a licensed electrician, safely routes generator power to your chosen circuits and prevents back-feeding electricity into utility lines — which can be dangerous for utility workers.
Does running on propane or natural gas affect my generator’s output? Yes. Generators running on propane typically produce about 10% less wattage than on gasoline. Natural gas can reduce output by 10–15%. If you plan to use an alternate fuel, factor this reduction into your sizing calculation.
What is the difference between a portable generator and a home standby generator? Portable generators are manually operated, require setup, and run on gasoline or alternate fuels. Home standby generators are permanently installed, activate automatically within seconds of an outage, and connect directly to your home’s electrical system and fuel supply. Standby generators require professional installation.
Using a Generator Sizing Tool
You’ve calculated your wattage needs — now use our Portable Generator Selector Tool to find the right generator in minutes. Simply make a few selections and you’ll receive tailored recommendations based on your specific power requirements.
After receiving your results, take a moment to review them. Consider the suggested sizes and think about potential future needs or additional devices you might want to add later. It’s wise to choose a generator that exceeds your calculated wattage by a safe margin for any unexpected surges. With these tips, you can confidently decide what size generator to run a house, ensuring reliable performance, a sound investment, and peace of mind.
Customer Support
Still unsure how much power you need in a backup generator? Our team is here to help you find the generator that fits your specific needs. Reach support by phone or live chat, or visit the Help Center for easy-to-follow guides and self-service tools. You can also check out our YouTube channel for tutorials and troubleshooting videos to help keep your equipment running smoothly.
