Home Generator Sizing Calculator
Use this calculator to estimate the total wattage required to power your essential home appliances during an outage. This will help you determine the appropriate size (in Watts or Kilowatts) for a home generator.
Common Appliances
Enter the quantity for each appliance you wish to power. Typical wattage values are pre-filled.
Other Appliances (Custom)
Add any other appliances not listed above. If an appliance doesn't have a starting wattage (e.g., resistive heaters, lights), enter the same value for both running and starting watts.
Understanding Home Generator Sizing
When the power goes out, a home generator can be a lifesaver, keeping essential appliances running and maintaining comfort. However, choosing the right size generator is crucial. An undersized generator won't be able to power your desired appliances, while an oversized one might be an unnecessary expense and consume more fuel.
Running Watts vs. Starting (Surge) Watts
The most important concept in generator sizing is the difference between running watts and starting watts:
- Running Watts (Rated Watts): This is the continuous power an appliance needs to operate once it's already on. For example, a refrigerator might continuously draw 150 watts.
- Starting Watts (Surge Watts): Many motor-driven appliances (like refrigerators, freezers, sump pumps, and well pumps) require a brief burst of extra power to start their motors. This surge can be 2 to 6 times their running wattage. This surge lasts only for a few seconds but is critical for the generator to handle.
Your generator must be able to supply enough running watts for all the appliances you want to operate simultaneously, PLUS enough additional wattage to handle the starting surge of the single largest motor-driven appliance that might kick on while everything else is running. Our calculator takes this into account by identifying the highest individual surge requirement and adding it to your total running load.
How to Use the Calculator
- Identify Essential Appliances: Think about what you absolutely need during a power outage. This might include your refrigerator, some lights, a TV, a furnace fan, or a well pump.
- Enter Quantities: For each common appliance listed, enter the number you wish to power. The calculator provides typical running and starting wattages.
- Add Custom Appliances: If an appliance isn't listed, use the "Other Appliances" section. You'll need to find its running and starting wattage (often found on the appliance's label, owner's manual, or manufacturer's website). If an appliance doesn't have a motor (like a coffee maker or incandescent light bulb), its starting watts will be the same as its running watts.
- Calculate: Click the "Calculate Generator Size" button.
Interpreting the Results
- Total Running Watts: This is the continuous power your generator needs to supply for all selected appliances running at the same time.
- Total Starting (Surge) Watts: This represents the maximum power spike your generator needs to handle when the highest surge appliance starts up while other appliances are already running.
- Recommended Generator Size: This is the larger of the two values (Total Running Watts or Total Starting Watts), indicating the minimum wattage capacity your generator should have. It's often recommended to add a 10-20% buffer to this number to account for future needs or unexpected loads.
Important Considerations
- Fuel Type and Capacity: Generators run on various fuels (gasoline, propane, natural gas, diesel). Consider fuel availability, storage, and consumption rates based on your expected run time.
- Portability vs. Standby: Portable generators are manually operated and can be moved. Standby generators are permanently installed, automatically turn on during outages, and are typically more powerful.
- Installation: For standby generators or connecting a portable generator to your home's electrical panel, professional installation with a transfer switch is essential for safety and compliance with electrical codes.
- Noise Levels: Generators can be noisy. Check the decibel rating, especially if you have close neighbors.
- Inverter Generators: These offer cleaner power (safer for sensitive electronics), are generally quieter, and more fuel-efficient, but often have lower wattage capacities and higher costs.
By carefully calculating your wattage needs, you can select a generator that provides reliable power for your home during emergencies without overspending.