The 3, the 5, and the 7 are how BMW sorts its cars

BMW's ordinary cars are named with a number. The 3 Series is the one the company is built around: a compact sporting sedan, and the pattern other makers were compared with for years. The 5 Series is larger. The 7 Series is the formal car, the one for the back seat as well as the driver.

The number is the map

Odd series numbers have been the cars. Even numbers, on many of the recent coupes and such, are a later habit, and we will not pretend the chart has always been tidy. What has stayed is the idea that you can tell the job of the car from the digit. A person who says "a Three" and a person who says "a Seven" are not talking about trims. They are talking about size and role.

The X models are the taller ones. The X5 is the line that made BMW an SUV maker as well as a sedan maker. We are not going to rank them here. We are going to use the names correctly when they come up, because a 3 Series and an X5 are different tools that happen to share a showroom.