To determine the handing of a door lock, stand outside of the room or building facing the door.

 If the hinges are on the left side of the door, the door is Left Hand (LH).

 If the hinges are on the right side, the door is Right Hand (RH).

handing of a door
  

A. A lock which by reversing the latch bolt, may be used by either hand (left or right).