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.
Calculator directory
Choose the right EV, solar, and battery calculator
EV charging time calculator
Enter your battery capacity, starting and target state of charge, and charger output to estimate charging time, the kWh pulled from the wall, and your cost per session — all from open, transparent formulas.
Open calculatorSolar panel calculator
Size a solar PV array from your daily electricity use, local peak sun hours, system losses, and panel wattage. Also estimates roof area and an off-grid battery bank using depth-of-discharge and round-trip efficiency.
Open calculatorBattery 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 calculatorEV road trip calculator
Estimate stops, charging time, and drive time from route distance, EV range, battery capacity, departure SOC, reserve SOC, target stop SOC and DC charger power.
Open calculatorSolar payback calculator
Apply the 30% federal ITC, model 0.5%/year panel degradation and 3%/year rate inflation, and see year-by-year cumulative savings until the system breaks even.
Open calculatorNet metering calculator
Compare a solar bill under traditional 1:1 net metering vs export-only credits (e.g. CA NEM 3.0). Get monthly net cost, exported kWh, self-consumption ratio, and annualized totals.
Open calculatorHeat pump vs gas calculator
Convert your annual heating demand to kWh and therms with COP and AFUE, then compare yearly fuel cost and CO₂. Uses EPA grid average 0.39 kg CO₂/kWh and 5.3 kg CO₂/therm.
Open calculatorGenerator sizing calculator
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.
Open calculatorSolar lease vs buy calculator
Model cash purchase (with 30% ITC) versus a 25-year lease with annual escalator. Inputs: system cost, lease payment year 1, escalator %, annual production, retail rate.
Open calculatorSolar panel tilt calculator
Get the year-round optimal tilt (≈ latitude), summer tilt (latitude − 15°) and winter tilt (latitude + 15°), plus expected production gain from seasonal adjustment.
Open calculatorSolar inverter sizing calculator
NREL and SEIA recommend a DC:AC ratio of 1.15–1.30. Higher ratios cost less per AC watt but cause midday clipping. Find the sweet spot for your location.
Open calculatorWind turbine calculator
Estimate annual kWh from rotor swept area, average wind speed, air density, capacity factor and turbine efficiency. Uses the Weibull-corrected power equation.
Open calculatorEV total cost of ownership calculator
Sum purchase price (minus federal tax credit), fuel/electricity, insurance, maintenance and registration over 5 years. Default electricity 4.0 mi/kWh, gas 28 mpg.
Open calculator