Recommended Generator Size: The minimum wattage your generator should provide, including a 25% safety buffer. This accounts for minor power spikes during normal operation.
Total Running Wattage: The combined continuous power draw of all selected appliances. This is the baseline load your generator must handle at all times.
Safety Margin (25%): An extra buffer added to the running wattage. Generators run more efficiently and last longer when they're not maxed out at full capacity.
Suggested Fuel Type: A general guideline based on size — portable gasoline units for small loads, dual-fuel options for mid-range, and propane or natural gas for large whole-house systems.
How This Calculator Works
You check off the appliances you want to power during an outage and optionally add custom items. The tool sums their running wattage and adds a 25% safety margin. It does not account for startup (surge) wattage, which can be 2–3 times higher for motor-driven appliances like refrigerators and pumps.
Quick Questions
What is the difference between running and starting wattage?
Running wattage is the continuous power an appliance needs. Starting (surge) wattage is the brief spike when a motor first turns on, often 2–3 times the running wattage. Your generator must handle the highest combined surge.
Why is there a 25% safety margin?
Running a generator at 100% capacity shortens its life and risks overloading during power spikes. A 25% buffer keeps the generator in a comfortable operating range and improves fuel efficiency.
Do I need a transfer switch?
Yes, if you're connecting a generator to your home's electrical panel. A transfer switch prevents dangerous backfeed into utility lines and is typically required by electrical code. Always hire a licensed electrician for installation.
How long will a generator run on a tank of fuel?
Runtime depends on the generator's tank size and load. A typical portable generator runs 8–12 hours at 50% load on a full tank. Larger standby units connected to propane or natural gas can run indefinitely with fuel supply.