The difference between Unisex and Girls styles:

A Unisex style is the standard type of t-shirts that are loose.

A Girl style is more form fitting designed specifically for a female body and is tighter around arms and waist.

Size Chart Men/Unisex Shirts       S   M   L   XL     Chest (inches)     34-36   38-40   42-44   46-48     Waist (inches)     30-32   32-33   33-34   36-38     Size Chart Girls Shirts       S   M   L         Size     0-2   4-6   8-10         Chest (inches)     30-32   32-34   36-38         Waist (inches)     25-26   27-28   30-32         Size Chart Kids     2 yrs   4 yrs   6 yrs   8 yrs   10 yrs   12 yrs           Weight (lbs)   31-34   35-41   42-45   49-52   54-62   62-75           Height (inches)   32-36   36-40   40-43   48-50   51-54   55-59           Chest (inches)   21   22   23   26   27   28         Chest: Measure under arms around the fullest part of the chest. Be sure to keep tape level across back and comfortably loose.   Waist: Measure around natural waist with a loose tape.