A lock backset is the distance from the door’s edge to the center of the bore hole or keyway — typically 2-3/8 or 2-3/4 inches.
For the full breakdown, see our best 2″ Backset Locks guide.
Most lock installations go wrong before the screwdriver comes out. Understanding what a backset on a lock is — the distance from the door’s edge to the center of the hardware’s bore hole — tells you exactly which lockset will fit your door without drilling new holes.
The backset decides where the knob, lever, or deadbolt sits on the door, and whether new hardware lines up with the door prep already drilled. Get the number wrong and the latch won’t reach the strike plate, the trim won’t cover the old holes, or you’re suddenly re-drilling a solid-core door. One careful measurement at the start prevents all of it.
What Exactly Does A Backset Measure?
A backset is the horizontal distance from the leading edge of the door to the center point of the lock’s bore, spindle, keyway, or follower — whichever part the hardware uses to turn the latch.
On cylindrical locksets — the common residential type — that means the round bore hole in the door’s edge. On mortise locks the reference point shifts: the measurement runs from the outside face of the forend to the center of the keyway or follower. Either way, you’re locating the middle of the hole, not its rim.
The same two numbers apply whether you’re fitting a knob, a lever, or a deadbolt. An exterior door often pairs a lever with a deadbolt, and both need a backset that matches the same prep.
The Two Standard Backset Sizes
Residential and commercial doors in the U.S. use one of two standard backsets: 2-3/8 inches (about 60 mm) or 2-3/4 inches (about 70 mm). Nearly every lockset sold at retail is built around one of those two numbers.
| Backset | Metric Equivalent | Typical Use |
|---|---|---|
| 2-3/8 in. | About 60 mm | Interior doors and many older exterior-door preps |
| 2
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