Cars come in all sorts of shapes and sizes. There are compact cars, medium size and large autos. Typical auto dimensions cars are at least 4900 mm long. They are not just longer than average cars; they are more spacious on the inside. Large cars also use powerful engines. Family size cars are either small medium or large. The large ones are almost comparable to a full size car.
Large family cars have room for five full grown adults. Cars 4800 long are considered large family size in the US and Europe. In Australia they are classified as medium size. Small and medium size family cars emphasize compactness. The large ones are noted for bigger trunks. This can be useful if you carry a lot of stuff with you.
Regardless of classification, variations in the size will be apparent. Physical size is not necessarily indicative of engine power. Sports cars for example, are very powerful.