Answer: Some of the confusion is because there is no cut and dried size definition from large shrub to small tree. This plant has a rounded more shrubby shape but it can get pretty big.
Also, plants tend to have a size range to which they mature. The ultimate size will depend on the climate and growing conditions, in Minnesota for instance this magnolia might only reach 8 or 10 feet tall, but it might be twice that height in Georgia. The width is usually described as being about 10 to 15 feet.
I realize those are big variations, but this plant can also be pruned to maintain a slightly smaller size. I would not recommend trying to keep it small enough to grow under a window, but a limited amount of size control can be achieved without making the plant look totally unnatural.
I hope this helps with your selection process.
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