RV generator calculator
One 13,500 BTU rooftop AC runs at about 1,500 watts and slams to 3,000 at start. That single number sizes most 30 amp rigs: a 3,400W inverter carries the AC itself, the 3,500 to 4,000W class adds the fridge and microwave, and a 2,200W suitcase only works with a soft start and discipline. Set your rig up below.
How RV sizing differs from house sizing
The rooftop AC dominates everything. It is the biggest load, it has the nastiest start surge, and in July it cycles all afternoon. So the method is the same worksheet math (running total plus the largest start spike) but in practice you are sizing to the AC and then checking whether the microwave fits beside it. On a 13.5k unit the surge is about double the running draw; a soft-start module cuts that surge by roughly 65% and is the single best dollar-per-watt upgrade in this hobby.
Two ceilings to respect. Your shore cord: 3,600W on a 30 amp rig, 12,000 on a 50, and the rig's main breaker enforces it whatever the generator can make. And campground rules: quiet hours make a 57 dB inverter worth more than its price difference over a 75 dB open frame.
Questions people ask
What size generator do I need for a 30 amp RV?
The 3,500 to 4,000W class is the practical answer for a 30 amp rig with one 13,500 BTU rooftop AC: the AC runs at about 1,500W but starts near 3,000, and the converter and fridge alongside push the peak to 3,900W. A 2,200W inverter starts that AC only with a soft-start kit installed and almost nothing else switched on. The shore cord itself tops out at 3,600W, so anything bigger than the 4,000 class is wasted weight.
What size generator for a 50 amp RV?
Plan on 5,500 to 7,000 watts if you run both air conditioners, which is the whole point of a 50 amp coach in summer. Two 13.5k units want about 3,000W running plus a 1,500W start margin, and the residential fridge and water heater in most 50 amp rigs stack on top. Paralleling two 3,400W inverters gets you there quietly.
Do soft starts really work?
Yes. A soft-start module ramps the compressor instead of slamming it, cutting the start surge by roughly 65%. It is the difference between a 13.5k AC starting on a 2,200W inverter or not, and around $300 installed. If you already own the small generator, the soft start is cheaper than the bigger generator.
Can I just use my RV’s shore power rating as the generator size?
It is the ceiling, not the answer. 30 amps at 120V is 3,600W and 50 amp service is 12,000W, but almost no rig actually draws its full service. Size to the loads you run at once, which the calculator does; buying a 12,000W unit for a 50 amp trailer that peaks at 5,000 buys noise and fuel burn, not comfort.