Circle: 4cm x 4cm
Original: 2.4cm x 3.2cm
Stadium: 2.4cm x 4.2cm
The width of the Original and Stadium are designed so they can go on the thin side part of over ear headphones (typically 2.5cm), and of course means they fit on many other items!
The Circle is slightly larger which makes it great for larger surfaces such as laptops and tablets.