How to Calculate What Size Generator You Need for Your Home

Understanding the right size for your whole house generator is crucial to ensure it meets your power needs without overspending on unnecessary capacity. At Texas Generator Pros, our detailed FAQ page on calculating generator size demystifies the process, offering step-by-step guidance to help you determine the perfect fit for your home. From assessing your essential power requirements to considering future needs, our resources are designed to empower you with the knowledge to make an informed decision.

Calculating Your Whole House Generator Size

Calculating the size of a whole house generator you need involves understanding your home's energy requirements during a power outage. Without the convenience of pre-made calculators, you can still estimate the appropriate generator size by following a systematic approach. Here's how you can do it:

Step 1: List Essential Appliances and Systems

Start by listing all the appliances and systems you consider essential during a power outage. Common essentials include the refrigerator, HVAC system, water heater, sump pump, lights, and specific outlets for charging devices. Remember, the goal is to maintain comfort and safety, not necessarily to power every aspect of your home as you would under normal conditions.

Step 2: Determine the Power Requirements

Each appliance and system on your list has specific power requirements, which are usually measured in watts. These requirements can typically be found on the appliance itself, in the user manual, or on the manufacturer's website. There are two key numbers to look for:

Starting Watts: The surge of power needed to start an electric motor. Appliances like refrigerators, pumps, and HVAC units require more power to start than to run.
Running Watts: The continuous power needed to keep the appliance running once it has started.

Step 3: Calculate Total Power Needs

Add up the running watts of all the appliances and systems you listed. Then, find the appliance with the highest starting watt requirement and add that to your total running watts. This gives you a rough estimate of the total wattage you need to power your essentials during an outage.

Example Calculation:

  • Refrigerator: 600 running watts + 2,200 starting watts
  • HVAC System: 1,500 running watts + 3,500 starting watts
  • Lights: 400 running watts (total for essential lighting)
  • Sump Pump: 800 running watts + 2,000 starting watts
  • Other essentials (charging devices, etc.): 500 running watts

Total Running Watts: 3,800 watts
Highest Starting Watts: 3,500 watts (HVAC System)
Total Power Requirement: 3,800 watts (running) + 3,500 watts (starting) = 7,300 watts

Step 4: Consider Fuel Type and Efficiency

Generators are available in various fuel types, including natural gas, propane, and diesel. The efficiency and availability of these fuels in your area can influence the size and type of generator you choose. Additionally, consider the generator's efficiency—how much fuel it consumes at a given load—as this will impact operating costs.

Step 5: Factor in Future Needs

Consider potential future needs or changes to your power requirements. If you plan to add more appliances or if your family grows, you might need more power. It's often wise to choose a generator with a slightly higher capacity than your current calculation suggests to accommodate future needs.


While this method provides a ballpark figure, consulting with a professional is crucial for an accurate assessment, especially to ensure safety and compliance with local codes. A professional can also advise on the best generator placement, fuel type, and installation practices to meet your specific needs. Remember, the goal is to ensure your home remains safe and comfortable during power outages, and choosing the right generator size is a critical step in that process.

Get Your Free Quote Today

If you're in the Greater Houston and Katy area and looking for a precise assessment of your home's generator needs, Texas Generator Pros is here to assist. Understanding the size of the generator you require can be complex, and it's essential to get it right for both safety and efficiency.

Our team of professional installers is ready to provide you with a comprehensive assessment and a free quote, ensuring you choose the perfect generator for your home. We specialize in helping homeowners like you prepare for power outages with confidence.

For a hassle-free consultation and to learn more about how we can support your needs, please visit our contact page to get in touch. Let Texas Generator Pros help you stay powered up, no matter what.