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Guide to Door Lock Measurements: Bore Size, Backset & Spacing
When replacing or installing a new door lock, there are a few key measurements you need to know before you place your order.
Lock Bore
The lock bore is the diameter of the hole for the lock body. The standard bore size is 2-1/8". Many older doors were drilled with smaller bores. Most modern locks require the standard 2-1/8" bore. MPLocks.com
If you want to replace the locks on doors with smaller diameter holes, you have two options:
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Re-drill the door to the standard 2-1/8" bore size.
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Use a lock designed for a smaller bore. A few lock companies, such as Weiser, still make locks to fit these smaller bores. MPLocks.com
Backset
The backset is the distance from the edge of the door to the center of the lock bore. The two standard backsets are 2-3/8" and 2-3/4". Other backsets include 2" (used by National and Lori Lock) and 5" (used by Weiser, Weslock, Kwikset, and others). MPLocks.com
Some brands, like Schlage, also offer latch extensions that allow you to position the lock closer to the center of the door. When replacing locks, the latch backset must match the holes already bored in the door. MPLocks.com
Lock Spacing
Lock spacing is the distance between two locks. When boring for a deadbolt above an existing knob or lever, there are two common standards for the spacing between the bottom lock and the deadbolt: 5-1/2" and 6", measured from the center of one bore to the center of the other. MPLocks.com
Specialty locks may use other spacing combinations. However, when adding a deadbolt lock, your best choice is usually one with a standard spacing measurement.