Cognomen Siz (Siz 
, Sitz 
, Сиз 
) , across the world, is quite a rare last name. The last name Siz is characteristic of Western Europe, particularly Luxembourg, where it is quite a rare surname, Austria, and Germany, where it is a rare surname. Measured by absolute frequency, the name is most common in the United States, Germany, and Kenya. Very seldom, Siz is the forename as well as the last name.