RV manufacturers state that RVs typically get between 6 and 12 miles per gallon. The type of RV, type of fuel and weight of the loaded RV all influence the mileage.
Class C RVs, which are built on a truck or van base, get better mileage than Class A RVs, which are built on commercial-type truck or bus frames. Class C motor homes average 8 to 12 miles per gallon. Class A motor homes average only 6 to 10 miles per gallon. Some Class A RVs use diesel fuel, which gives them slightly better mileage. Class B RVs are small motor homes that are actually modified vans. They get much better mileage rates, similar to any large van, averaging between 18 and 25 miles per gallon.