In order for a cylindrical lock to fit in the door, a bore must be cut into the door. A standard bore is 2-1/8” in diameter.
Typically, a single bore is cut 38” up from the bottom of the door. If a deadbolt is also being added to the door, a double bore will be cut into the door face.
The distance from the edge of the door to the middle of the bore is called the backset. The two common backsets are 2-3/8” and 2-3/4”. Some door styles are limited in the backset that can be used.