Generac Generator Size Calculator
Use this calculator to estimate the appropriate Generac generator size (in kilowatts) needed to power your home or business during an outage. Accurately sizing your generator ensures you have enough power for essential appliances without overspending on an oversized unit.
1. Select Your Essential Appliances & Loads
Check the appliances you wish to power and specify the quantity. Typical wattage values are provided, but you can adjust them for custom items.
None
3-Ton (4500 Running W / 13500 Starting W)
4-Ton (6000 Running W / 18000 Starting W)
5-Ton (7500 Running W / 22500 Starting W)
(1000 Running W / 3000 Starting W)
(4500 Running W / 0 Starting W)
(3000 Running W / 0 Starting W)
(5000 Running W / 0 Starting W)
(800 Running W / 2400 Starting W)
(500 Running W / 1500 Starting W)
(800 Running W / 2400 Starting W)
(1000 Running W / 0 Starting W)
(1500 Running W / 0 Starting W)
(1000 Running W / 2000 Starting W)
(1000 Running W / 0 Starting W)
2. Add Custom Appliances (Optional)
Estimated Generac Generator Size:
Based on your selections, you would need a generator with a minimum capacity of: 0 kW.
This estimate includes a 10% safety buffer and accounts for the highest starting wattage of a single motor-driven appliance.
Understanding Generac Generator Sizing
Choosing the right size generator for your home or business is crucial for reliable backup power. An undersized generator won't be able to power all your essential appliances, while an oversized one can be an unnecessary expense and less fuel-efficient. Generac, a leading manufacturer, offers a range of generators, and this calculator helps you narrow down the ideal size.
Why Proper Sizing Matters
- Avoid Overload: An undersized generator will trip its breaker or struggle to start motor-driven appliances, leaving you without power when you need it most.
- Prevent Damage: Consistent overloading can damage the generator and potentially the appliances connected to it.
- Cost Efficiency: An oversized generator costs more upfront, consumes more fuel, and may not operate at its most efficient load, leading to higher running costs.
- Longevity: A properly sized generator operates within its design parameters, leading to a longer lifespan and fewer maintenance issues.
Running Watts vs. Starting Watts: The Key Difference
The most critical concept in generator sizing is understanding the difference between running watts and starting watts:
- Running Watts (Continuous Watts): This is the power an appliance uses continuously once it's operating. For resistive loads like lights or electric heaters, running watts are the only consideration.
- Starting Watts (Surge Watts): Appliances with electric motors (e.g., refrigerators, air conditioners, well pumps) require a significant burst of extra power for a few seconds to get the motor running. This surge can be 2-3 times their running wattage. A generator must be able to handle this highest single surge while still powering other continuous loads.
Our calculator takes both into account. It sums the running watts of all selected appliances and then adds the additional surge required by the single largest motor-driven appliance you plan to run.
How the Calculator Works
This calculator estimates your total power requirements by:
- Summing the continuous running wattage of all selected appliances.
- Identifying the appliance with the highest starting (surge) wattage.
- Calculating the total power needed by adding the highest starting wattage to the running watts of all other appliances. This ensures the generator can handle the largest motor starting while everything else is running.
- Adding a 10% safety buffer to account for minor fluctuations, future additions, or unexpected loads.
- Converting the final wattage to kilowatts (kW), which is the standard unit for generator sizing.
Tips for Accurate Sizing
- Prioritize: Decide which appliances are absolutely essential during an outage (e.g., refrigerator, furnace, well pump) and which are optional.
- Check Appliance Labels: For precise figures, look at the data plate or owner's manual for your specific appliances. The wattage listed is usually the running wattage.
- Consider Future Needs: If you plan to add new appliances or expand your home, factor in a little extra capacity.
- Professional Assessment: For whole-home backup solutions, it's always recommended to consult with a certified electrician or Generac dealer. They can perform a detailed load analysis of your home's electrical system.
Use this tool as a helpful guide, but always verify your specific needs with a qualified professional before making a purchase decision.