When calculating what unit you need you should consider what the draw in amps is and multiply that by 100. It is not exact but it is a good rule of thumb. So an air conditioner that draws 18 amps and a 1000 watt microwave will need 2800 watts. Remember that the conversion is not exact, You should allow for a 10% buffer. In this example, the 2800 watts could actually be closer to 3000 to 3100 watts of draw and would tax a 3000 watt generator. Common sense would say to shut the a/c off while using the microwave and then turn it back on when you are done cooking. A RV that has a 30 amp plug should be able to be powered by a 3000 watt generator. A RV that has a 50 amp plug would require you to look at what is being used and restrict some uses when using a 3000 watt generator to keep from burning the generator up.