The Field Calculators → Power
Power
Generator sizing & fuel burn
What size you need, how long the fuel lasts, and the test that tells you the truth about it.
Result
Running watts needed3000 W
Largest motor starting surge4500 W
Hours per day you'd run it6
FuelGasoline (~4.5 kWh per gallon)
Fuel on hand25 gal
Generator size
5,400 W
Covers the 4,500 W peak with 20% headroom.
Fuel burn
4.00 gal/day
18.0 kWh per day at 6.0 hrs.
Your fuel lasts
6.3 days
For 14 days you'd need
56 gal
Running cost per kWh
— depends on fuel price
Multiply gal/day by your price and divide by kWh/day.
What this will not do
- Test by amps under load, never by volts unloaded. An unloaded generator shows perfect voltage right up until it can't carry anything. Put a clamp meter on the output with the real load running — that one habit saves days of chasing ghosts.
- A transfer switch, installed by an electrician, is not optional. A backfeed or 'suicide' cord energizes the line outside your house and can kill the crew fixing it.
- Carbon monoxide kills people every storm season. Generator outside, well clear of windows and doors, and a CO alarm in the house. An open garage door is not ventilation.
- Gasoline goes stale in months. Stabilize it, rotate it, and exercise the generator monthly under load — an unexercised generator is a decoration.
The full build and the reasoning are in Chapter 42 of the guide.