Overall average size of an RV is 8.5 feet wide, 25 feet long, 9 feet high.
Each RV class has different dimensions such as:
Class A average dimension is 8.5 feet width, 40 feet length, 10 feet height. They can expand wider with slide outs.
Class C average 8.5 feet wide, 28 feet long, 10 feet high.
Class B average 20 feet long, 8 feet high, 8.5 feet wide.
Travel trailers average 11 feet high, 32 feet long, 8 feet wide.
RV Industry Association Max motorhome length is 45 feet, width is 102.
Note some National Parks limit size to 28 feet long or less.
Some highways in the US have a 8.5 feet width limit.