Many definitions define the coupe as a two- or three-door model, while a sedan almost always has four doors. Actually there are four-door coupes, and two-door sedans, so the differences between a coupe and a sedan automobile may not always be quite clear. In reality, a coupe is strictly defined by its interior volume or space.
The real distinction between a coupe and a sedan has little to do with doors and are made clear by the Society of Automotive Engineers (SAE), which standardizes definitions of the different types of cars on the market. Measurements of these cars are as follows:
- A coupe has an interior space of less than 33 cubic feet (0.934 cubic m).
- A sedan has an interior that is equal to or greater than 33 cubic feet (0.934 cubic m).
As a result, volume alone is the real difference. A two-door car with a large interior space is essentially a two-door sedan. Likewise, a four-door car with a small volume is a four-door coupe.
Nevertheless, many manufacturers call a car a coupe when they want to evoke a sportier concept for it. The term may even be part of the name, even though technically, the buyer is really getting a sedan. The Cadillac Coupe de Ville is a classic example of what is really a two-door sedan. It can be difficult for most people to determine what the car really is when the word "coupe" is added to the name.
Some people mistakenly think a coupe and a sedan are differentiated by whether the car has a hatchback. While it is true that many coupes have these rear openings, and are sometimes referred to as a three-door car, not all do. Some have a traditional trunk. Further, there are four-door coupes and four-door sedans with a hatchback, which are more properly called station wagons.
It is also not true that these cars can be distinguished by counting the number of seats. Some people define coupes as having merely front seats, and possibly a removable back seat. Actually, coupes can have two rows of seats or one. In contrast, the sedan always has two rows of seats, but the distinction between a coupe and a sedan can’t be made here because of the variation of rows of seats in the coupe.
The best bet is for people who want to know the difference to stick with the car’s interior volume, rather than worrying about what the car is named. When choosing a car, most consumers find that it doesn't really matter little what it is called. Usually what does matter is the car’s performance, space for passengers, and ease of use.