Free calculator

RV Generator Size Calculator: What Size Generator Do I Need?

Tick what you want to run at the same time. The calculator adds the running watts, adds the biggest startup surge, adjusts for altitude, and tells you which generator class covers it.

What runs at the same time
ApplianceRunning WStarting W

Typical values: your appliance’s data plate is the real number. Starting watts apply to motors and compressors only.

Your setup

You need

–generator class

  • Running load–
  • Peak at startup–
  • Altitude loss–
  • 30A shore limit3,600 W

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How the calculation works

  1. Add the running wattsEverything you want on at the same time.
  2. Add the biggest startup surgeOnly the single largest extra surge (starting minus running watts), because motors rarely start at the same instant.
  3. Correct for altitudeRoughly 3.5% less output per 1,000 feet for gas generators.
  4. Leave about 10% headroomRunning a generator flat out shortens its life and makes it louder.

Typical RV appliance wattage

ApplianceRunningStarting (peak)
Roof AC, 13,500 BTU1,300 W2,800 W
Roof AC, 15,000 BTU1,600 W3,500 W
Second roof AC, 13,500 BTU1,300 W2,800 W
Microwave (1,000W cooking power)1,500 W1,500 W
Converter / battery charger500 W500 W
Electric water heater element1,400 W1,400 W
Residential fridge200 W800 W
Coffee maker900 W900 W
Hair dryer1,500 W1,500 W
Electric space heater1,500 W1,500 W
TV and electronics150 W150 W
Laptop and phone charging100 W100 W

Getting more from a smaller generator

  • Fit a soft start on the AC. It is often the difference between needing a 3,000W-class generator and a 2,200W-class one.
  • Don’t stack big loads. Run the microwave or water heater element when the AC compressor is off.
  • Two inverter generators in parallel give you the power of a large one in two portable pieces.

Models compared in best RV generators, background in the RV generators guide.

Frequently asked questions

What size generator do I need to run an RV air conditioner?

A 13,500 BTU roof AC typically runs at about 1,300W but needs roughly 2,800W for a moment to start the compressor. Plan on a 3,000W-class generator, or a 2,200W-class inverter generator if you fit a soft-start device, which cuts the startup surge substantially. A 15,000 BTU unit needs more.

Will a 2,000-watt generator run my RV?

It runs lights, the converter, a TV, the fridge and small appliances. It usually won't start a roof AC on its own; with a soft start, a 2,200W-class inverter generator often can, but not while you also run the microwave or a water heater element.

What is the difference between running and starting watts?

Running watts are what an appliance uses continuously. Starting (surge) watts are the short spike when a motor or compressor starts, often two to three times the running watts. A generator must cover your total running load plus the biggest single starting surge.

Does altitude affect generator power?

Yes. Gas generators lose roughly 3-4% of their output for every 1,000 feet above sea level, so a generator that just covers your load at sea level may fall short in the mountains.

30-amp or 50-amp: what can my RV draw?

A 30-amp RV can draw up to about 3,600W from shore power or a generator; a 50-amp RV has two 50A legs, up to about 12,000W. A generator smaller than your service still works as long as you manage what runs at once.

Estimates only. Appliance draw varies by model and condition; check data plates and your generator’s rated (running) and surge output.