⚡ Generator Backup Sizing Calculator

— kW
Rec. Size
— hrs
Fuel Runtime
$—
Daily Fuel Cost
$—
System Cost
— W
Critical Loads
— hrs
Battery Backup
1
Critical Loads
Load Name Watts (W) Qty Hrs/Day Daily kWh On?
Motor loads (well pumps, fans) draw 3–6× their running wattage at startup. The 1.5× surge factor here is a conservative estimate — size up if you have large motor loads.
2
Existing Battery Bank (Optional)
If you have a solar + battery system, your generator only needs to cover the shortfall and recharge batteries. Enter 0 for battery capacity if no battery bank exists.
3
Generator Sizing
80% Load Rule: Run generators at 50–80% of rated capacity for best efficiency, longevity, and to avoid wet-stacking (diesel). Avoid running at less than 30% load for extended periods.
4
Fuel Consumption & Runtime
5
Outage Preparedness Summary
Critical Loads Covered
Runtime on Fuel
📅 Days Until Refuel
💰 Monthly Fuel Cost