Backsets, Strikes, and Latch Hardware

Two measurements decide whether a lock fits a door: backset and door thickness. Get either one wrong and the latch won’t line up with the strike, the door won’t latch, and the hardware goes back in the box. This guide is for contractors and serious DIY builders specifying or replacing locks, latches, and strikes — the folks who can’t afford a second trip to the counter.

For related product information, see Locksets and Push/Pulls: How to Choose the Right Door Hardware.

Start with the term that trips up most buyers. Backset is the horizontal distance from the door edge to the center of the lock bore hole. Measure it straight across the face of the door, not wrapped around the edge. Two standard sizes cover nearly all residential work. For residential doors, 2-3/8 inches is standard for interior doors, while 2-3/4 inches is standard for exterior doors. Deadbolts usually run 2-3/4 as well. Commercial settings typically use 2-3/4 inches. One rule above all: measure precisely from the door edge to the bore center; do not round.

Measure the Slab, Then the Backset

Door thickness is its own measurement and it controls whether the lock can physically connect through the slab. Standard hardware typically fits doors 1-3/8 to 1-3/4 inches thick. Measure the slab only — not the jamb, the casing, or the trim. Thicker slabs need a thick door kit, and a lock that ignores thickness simply won’t reach.

Here’s the smart hedge against a measuring mistake. Adjustable latches allow switching between 2-3/8 and 2-3/4 inches. Western Building Center’s lineup includes that exact kind of flexibility — a 6-way adjustable deadlatch from Kwikset and a universal deadbolt latch both cover the common backsets without forcing a guess at the counter. Deadbolts behave differently, though. Their backsets are almost always fixed, because the bolt mechanism sets the geometry and there’s nothing to slide.

Mortise locks are their own animal. For mortise locks, backsets vary, commonly 2-1/2 or 2-3/4 inches, requiring precise manufacturer templates. They need a rectangular pocket cut to an exact template. Verify the template before you order — there’s no fudging a mortise pocket after the fact.

Door type	Standard backset
Interior residential	2-3/8” (60 mm)
Exterior residential / deadbolts	2-3/4” (70 mm)
Commercial cylindrical	2-3/4”
Mortise	Commonly 2-1/2” or 2-3/4” (template-specific)

Measurement	What to check
Backset	Door edge to bore center, straight across
Door thickness	Slab only, 1-3/8” to 1-3/4” standard
Over 1-3/4” thick	Requires a thick door kit

Strikes, Keepers, and Alignment

The strike is the small part that causes the big headaches. A common sizing reference for cylindrical and mortise locksets is the ANSI standard strike at 1-1/4” x 4-7/8”. WBC’s strike selection runs from a 1-1/4-inch lip strike to a 2-1/4-inch extended-lip strike with a radius corner, plus a Kwikset strike plate sized to match Kwikset locksets.

Getting the strike to line up is the whole game. Align the latch with the center of the strike opening; the bolt must slide in without scraping. If it catches the frame, adjust the strike or file slightly. That’s a normal part of the job, not a sign something’s wrong.

Windows split along a clear line. Vinyl windows use nylon keepers; wood windows need metal. The right-hand vinyl keeper made for multipoint locks is made for multipoint locks on vinyl windows, measures 5/8” wide, 1-13/16” long, and 7/16” thick with screw holes at 3/4” centers, and is made of nylon/plastic intended for use on vinyl windows only. Put a nylon keeper on a wood window and it won’t hold — for wood windows, a metal version is generally required.

Electric strikes are not a swap-in part. Electric strikes must match your specific lock body — cylindrical, mortise, or rim exit — and the frame cutout, as they are not interchangeable. Match the lock body and the cutout before ordering, every time.

Handing: Stand Outside and Look at the Hinges

Levers, mortise locks, entry handlesets, and split-finish sets all care about handing. Round knobs and standard passage sets usually don’t. The method is simple: stand on the outside of the room and look at where the hinges sit. Hinges on the left means left-hand. Hinges on the right means right-hand. Strikes and keepers can be handed too — that vinyl window keeper above is right-hand only and its right-handed design means it is only compatible with right-hand operation windows. Order the wrong hand and it installs backward.

A Montana Note on Seasonal Fit

Wood doors and frames move with the seasons. Humidity swells the slab in the warmer months; cold and dry weather shrinks it. A lock that latched clean in July can bind in January, or a strike that lined up in winter can drift by summer. Check latch-to-strike alignment seasonally and keep hinge screws snug. When the bolt starts scraping, that’s the cue to adjust or file the strike a hair — same fix as a fresh install, just prompted by the weather.

Frequently Asked Questions

What is backset and how do I measure it? Backset is the horizontal distance from the door edge to the center of the lock bore hole, measured straight across the face of the door rather than wrapped around the edge. Measure precisely to the bore center and do not round — rounding is what causes the latch to miss the strike.

What’s the difference between 2-3/8” and 2-3/4” backset? 2-3/8 inches (60 mm) is the standard for interior residential doors. 2-3/4 inches (70 mm) is standard for exterior doors and most deadbolts, and it’s also the common size for commercial cylindrical locks.

Can one latch fit both backsets? Many quality locksets ship with an adjustable latch that switches between 2-3/8 and 2-3/4 inches, which is the easiest way to hedge against a measuring error. Deadbolts are the exception — their backsets are almost always fixed because the bolt mechanism sets the geometry.

How thick a door will standard hardware fit? Standard hardware typically fits doors 1-3/8 to 1-3/4 inches thick. Measure the slab only, not the frame or trim. Anything over 1-3/4 inches needs a thick door kit.

What size is a standard strike? A common ANSI strike dimension for mortise and cylindrical locksets is 1-1/4” x 4-7/8”. Match the strike to the lockset, then align the latch with the center of the strike opening so the bolt slides in without scraping.

Why won’t a vinyl window keeper work on a wood window? Vinyl window keepers are made of nylon/plastic and are intended for vinyl windows with multipoint locks only. Wood windows generally require a metal strike instead.

How do I figure out door handing? Stand on the outside of the room and look at the hinges. Hinges on the left means left-hand; hinges on the right means right-hand. Most round knobs and passage sets are non-handed, but levers, mortise locks, handlesets, and some strikes and keepers are handed and must match.