To determine the proper size generator for your RV you need to know how much electrical power you will use.
1. Determine what electrical devices you will want to run from the generator. Survey your RV for appliances that run on 120 volts. TV, microwave and other kitchen appliances generally require the most power but smaller appliances can add up. Most RV lights are 12 volt but some may be 120 volt. Your RV A/C is the biggest power user.
2. Add up the power requirements, in watts, for all the devices that you are likely to operate at the same time. Wattage ratings are printed on light bulbs; other devices like hair dryers and electric heaters are also described by their wattage requirements. If the device doesn’t provide a wattage requirement, you can determine watts by multiplying volts times amps. If you just can’t find the power requirement of a device, you can use this RV Appliance Wattage Chart (Remember, the chart is just a guide; actual wattage requirements vary significantly among brands and types.) Be aware that some electrical devices have starting wattage requirements that are larger than the running watts. An RV air conditioner is one such appliance. Use the starting wattage requirement when applicable. and the running watts for all other devices.
3. Add together the wattage requirements for all the electrical devices that you want to use at the same time. This is the minimum wattage you will need from a generator.
You should consider a generator with a power rating somewhat higher than your minimum requirement so the generator doesn’t have to work at full capacity.
It is possible to get along with a smaller generator since you don’t really need to run everything at the same time. But you’re not likely to want to turn off the TV when you use the microwave. And it is likely you’ll want to use a toaster or coffee maker while running the microwave.
You may also want to read: RVing with a Portable Generator