Determine the ideal generator size for your home or business by listing the appliances you plan to power. This calculator considers both continuous running wattage and the higher surge (starting) wattage required by motor-driven appliances.
Your Appliances:
Appliance
Running Watts
Starting Watts
Quantity
Generator Sizing Results:
Total Continuous Running Watts Required: 0 Watts
Peak Starting Watts Required (Surge): 0 Watts
Recommended Generator Size: 0 Watts
Recommended Generator Size: 0 kVA (assuming 0.8 power factor)
Note: A 20% buffer has been added to the peak starting wattage for safety and efficiency.
Choosing the right size generator is crucial for ensuring your essential appliances run smoothly during a power outage or for providing power in off-grid situations. An undersized generator won't be able to handle the electrical load, potentially damaging itself or your appliances. An oversized generator, while capable, will consume more fuel than necessary and might not operate at peak efficiency.
Running Watts vs. Starting Watts
Running Watts (Continuous Watts): This is the power an appliance uses continuously once it's turned on and operating normally. For example, a light bulb uses its rated wattage constantly.
Starting Watts (Surge Watts): Many motor-driven appliances (like refrigerators, air conditioners, well pumps, and power tools) require a brief burst of extra power to start their motors. This surge can be 2 to 3 times their running wattage. Once the motor is running, the power demand drops back to the running wattage.
How the Calculator Works
This calculator determines your total power needs by summing the running watts of all appliances you wish to power simultaneously. It then identifies the single appliance with the highest starting wattage requirement. The generator must be capable of handling the combined running watts of all active appliances PLUS the surge from that one largest starting appliance. This ensures that when a motor-driven appliance kicks on, the generator can provide the necessary temporary boost without tripping or stalling.
A 20% buffer is automatically added to the calculated peak wattage. This buffer provides a safety margin, accounts for potential future additions, and helps prevent the generator from running at its absolute maximum capacity, which can extend its lifespan and improve fuel efficiency.
Watts vs. kVA
Generators are often rated in both Watts (W) and kilovolt-amperes (kVA).
Watts (W): Represents the "real power" or the actual power consumed by an appliance to do work.
kVA (kilovolt-amperes): Represents the "apparent power," which is the total power in an electrical circuit. It's a combination of real power (Watts) and reactive power (VARs).
The relationship between Watts and kVA is defined by the power factor (PF): Watts = kVA × Power Factor. For most residential and small commercial applications, a power factor of 0.8 is commonly assumed. Therefore, to convert Watts to kVA, we use the formula: kVA = Watts / (1000 × 0.8).
Tips for Accurate Sizing
Identify Essential Appliances: List only the appliances you absolutely need to run during an outage.
Check Appliance Labels: The most accurate wattage information can be found on the appliance's data plate or owner's manual.
Stagger Appliance Starts: If you have multiple motor-driven appliances, try to start them one at a time to avoid exceeding the generator's surge capacity.
Consider Future Needs: If you anticipate adding more appliances later, factor that into your initial sizing.
Consult an Electrician: For whole-home backup systems or complex setups, always consult a qualified electrician.