Camping inverter generator
Fridge 150 W + lights 60 W + laptop 80 W + 1 kW microwave (starts at 1500 W). Honda EU2200i (1.8 kW continuous) handles it.
Generator sizing calculator
What size generator do I need?
List your running watts and the largest motor (well pump, AC compressor, fridge), apply LRA-based starting surge, and add a safety factor for fuel headroom and altitude derating.
Generator Sizing
Standby generator sizing
Recommended generator9,000 W
Continuous requirement7,200 W
Peak surge requirement9,000 W
Results are first-pass estimates. Verify with installers, manufacturers, and utility tariffs before purchase.
How it works
How it works
- Continuous load = sum of running watts of all simultaneous loads.
- Starting surge = largest motor running W × LRA factor (3× for inverter drives, 5× for capacitor-start motors).
- Required kW = (continuous + surge) × (1 + safety%) / 1000. Add 3% per 1,000 ft above sea level for naturally aspirated engines.
Worked examples
Worked examples
Suburban portable, well + fridge
8,200 W continuous + 4,500 W surge for 1.5 hp well. Pick 9–10 kW (Generac 7676 or DuroMax 12 kW).
Whole-home standby
18 kW continuous + 6 kW HVAC surge → Generac 24 kW (Guardian 7210) or Kohler 26 kW.
Generator FAQ
Generator FAQ
Running vs starting watts?
Running watts is steady-state. Starting watts is the surge to spin a motor — typically 3–7× running. Generators specify both.
Do LEDs and electronics need surge?
Negligible — resistive and switching-supply loads draw nameplate or less. Only motors (compressors, pumps, well, AC) need surge headroom.
Inverter vs conventional?
Inverter generators produce <3% THD safe for electronics; conventional generators are 8–25% THD and louder. Inverters cost 30–50% more for the same kW.
Why a safety factor?
Generators derate ~3%/1000 ft elevation and ~1%/°C above 25 °C. A 20% safety factor covers both plus future load growth.
Backup Power Calculators
Battery & Generator Backup Calculators
Battery runtime calculator
Enter your battery capacity in watt-hours, the running load, idle standby draw, usable depth-of-discharge, and inverter efficiency to estimate practical runtime for a Jackery, EcoFlow, Bluetti, APC UPS, or any custom 12 / 24 / 48 V bank.
Open calculatorHome battery backup calculator
Add up critical loads (fridge, well pump, internet, a few lights), pick how many hours per day you need them, set a target number of backup days, and the calculator returns the battery bank size and how much solar recharge offsets the draw each day.
Open calculator