This means a skill with a radius of 12 yards will go passed the edge of the screen from left to right by 365 yards on each side and passed the edge of the screen from top to bottom by 5 yards. Enemies closest attack in melee can only be used if 1 yard away or less from the player.
While based on the real unit of measurement of three feet or 9144cm the in-game.
Diablo 2 yards radius. Walk Run Speed. Yards are a unit of distance used in Diablo II and Diablo III. In 640×480 resolution the screen is 133×18 yards.
Same for the closest melee skills from the player The players hit box has a 1 yards radius. In 800×600 resolution the screen is 167×23 yards.