Here's some info I found helpful:
Doorknob measurements are fairly standardized, but there are still a number of variables to consider. The standard measurements for doorknobs will depend on the answers to these questions:
· Is the door interior or exterior?
· Is the door blank or pre-drilled?
· Are you replacing an existing doorknob?
To speak the language of doorknob installation, these are the terms to know:
· The bore hole is the doorknob hole.
· The cross bore is the hole that goes from the narrow edge of the door to the doorknob hole.
· The backset is the distance from the edge of the door to the center of the bore hole.
· The latch is the part of the hardware that goes into the cross bore hole. These come in three varieties: drive-in, rounded corner and square corner.
· The shank, or spindle, is the part of the hardware that goes through the door, connecting the knobs on either side.
· A handleset is hardware for an exterior door that includes a keyed deadbolt separate from the knob or lever.
Standard Measurements for Doors and Knobs
When choosing a doorknob — which generally comes in a set including knobs, shank and latch — focus on three key measurements: the thickness of the door, the backset and the size of the bore hole. Most interior doors are 1-3/8″ thick, while exterior doors are typically 1-3/4″ thick. The most standard backset for a door is 2-3/8″, but some doors (particularly exterior) have a 2-3/4″ backset. The standard cross bore has a diameter of 1″. The standard shank size of a doorknob is 1/4″.
The standard diameter of the bore hole is 2-1/8″. If you will be using a hole saw to drill the bore hole, the standard height is a bore hole centered on 36″ from the bottom of the door. In new construction, doors are hung so that the bore hole is centered on 40-5/16″ above the finished floor.
If using a separate deadbolt for an exterior door, the bore hole should be either the standard 2-1/8″ or 1-5/8″ diameter. Handlesets that are one piece require two bore holes — one above the other and typically 5-1/2″ apart center to center.