Most interior handle swaps take twenty minutes. The other half take three hours and a new door, and the difference comes down to one measurement: the backset. Get it wrong and the latch never reaches the strike. Here is how to check it before you buy, scribe the latch plate, and set a strike that reaches framing.
This page covers the hardware only. If the door is not hung yet, start with how to install an interior door.
Know the Three Hardware Parts and the One Number That Decides What Fits
The latch is the moving bolt on the door edge, the part that reaches into the frame.
The rose and spindle is the pair of handles joined by a shaft that carries the turn through the door to the latch. The roses sit on the flat faces.
The strike plate is the flat plate on the jamb, with a shaped opening the latch enters. It screws to the frame, not the door stop.
Two more terms matter. The round hole through the door faces is the face bore. The hole cut into the edge of the door is the edge bore. They have to line up, and their relationship to that edge is the backset measurement.
That backset distance runs from the door’s edge to the center of the spindle hole. Measure yours and you know what fits.
This Old House puts interior backset at 2 3/8 inches and exterior backset at 2 3/4 inches.
Dunn Lumber says something different. Their guide calls 2-3/4 inch the most common measurement, then warns that not all doors are drilled that way and you must match the replacement to your door.
- Take the existing handle off, or find the edge of the face bore on the door edge.
- Measure from the door edge straight across to the center of that bore.
- Get 2 3/8, This Old House’s interior figure, and you need 2 3/8 inch backset. Get 2 3/4, the exterior figure, and you need 2 3/4.
Also measure the door’s thickness. A spindle has to cross the door and still let the roses screw down tight. Thin hollow core and thick solid core will not take the same set.
Knob Height and the Order of Operations: Which Steps Come First
Knob height is the second measurement worth getting right. This Old House gives 36 inches from the finished floor as the standard, and says the reason to adjust is to center the knob on the panel.
On a solid-core four-panel door, their general contractor Tommy Silva moved the knob height to 37 inches to sit on the middle rail of the stile. The same page says to check other knobs in the house and keep the height consistent.
Now the sequence. This Old House lays it out in a specific order, and the order matters.
- Mark the face at knob height, using the template if the new hardware came with one.
- Drill the face bore through both faces of the door.
- Drill the edge bore into the door edge.
- Scribe the latch plate so it fits the door edge.
- Cut the latch mortise and install the latch assembly.
- Fit the handles and spindle, then fasten the face plate.
Most locksets ship with a cardboard template for lining up the two bores. Use it.
One prep step makes the rest easier. This Old House opens the door halfway and taps two shims, one from each side, between the floor and the door bottom to hold it steady.
Scribing the Latch Plate: Why a New Latch Binds
This is the step most beginner guides skip, and it is why a new latch binds.
The latch plate is a rectangle of thin steel that sits flush in a shallow recess on the door edge. If the recess is too shallow, the plate stands proud and the latch fouls the strike.
Bob Vila describes the fix. Most doors come with space removed for the face plate. If not, trace the plate onto the door, centered and level, then remove wood with a chisel so the plate sits flush.
That is the scribing. Mark the plate outline and cut the recess so the steel sits level with the wood, not above it.
First, the bevel. The latch bolt is wedge shaped, and the tapered side has to face the door frame.
Bob Vila is blunt about it: get the bevel backwards and you must turn the handle to close the door each time. HGTV says the tapered side of the turning lock should face the strike plate, and wikiHow says a wrong-way bevel gives you difficulty closing.
Second, drive-in screws. If the new plate comes with screws that tap into the door edge rather than screw into a hole, you are meant to drive them, not turn them.
wikiHow puts a block of wood on the latch and taps it with a hammer until the latch back reaches the end of the hole.
Third, timing. Wait until the handles are installed before you tighten the face plate. The latch must align with the spindle first.
When the Strike Plate Does Not Reach the Framing
The strike is not just a plate on the jamb face. It has a deeper lip that reaches past the jamb into the framing, and that lip is what the latch bolt pushes against.
That is why strike screws can spin in a hollow jamb and never tighten. Screwed into the thin face of the jamb only, the plate never firms up and the door never latches.
Dunn Lumber’s guide covers adjusting the strike, and its sequence for replacing a broken latch works as well for a new style of handle.
- Identify the problem first, because every door has its own version of it.
- Remove the inside handle, then the outside handle.
- Remove the latch and fit the new one.
- Reattach the handles.
- Adjust the strike last.
That last step is the one people skip, and it separates a door that latches from one you have to pull.
One more from Dunn Lumber: pick a latch that is the same brand as the existing one, stamped on the latch itself. A dead latch, their term for the exterior two-part type, is not for an interior door. For exterior and window hardware as a family, see our window and door buying guide.
When New Hardware Will Not Fit the Door
The backset is not standard. You measure your door and the number does not match the two you see in the aisle. There may be no standard knob in that size.
Adjustable-backset hardware uses a longer latch body with a movable spindle to cover a wider range, or you replace the door.
The door edge has no room for the latch. On a hollow-core door with no lock block, the edge is thin and the latch has nothing to grip. Add a reinforcing plate behind the edge, or use a surface-mounted latch. On a narrow door near a jamb there may be no edge space.
The bore is in the wrong place, usually because the door was re-hung or the knob moved. The handle has to reach the bore. Fill the old hole and drill a new one, but on solid core that means chiseling a fresh mortise.
The door is too thin for the mechanism. If the spindle cannot span the door without the roses bottoming out, the set will not work. Thicker doors also need longer screws to bite into the lock block.
Every one of those fixes has the same shape: adjust the door, or accept the door. If you hang the door as well as the hardware, that changes the arithmetic, and how to install a prehung interior door covers the frame side.
If the hardware is fitted correctly and the latch still will not catch, the cause is usually the door or frame moving. That is a different diagnosis, and how to fix an interior door that will not close covers it.
Choosing a Privacy Latch or a Passage Latch: Which One Fits
One question decides this: does anyone need to lock the door from the inside?
A privacy latch suits a bathroom or a bedroom, with a push button or turn that locks from the inside and no keyed cylinder outside. It gives privacy, not security against a determined intruder.
A passage latch suits a closet or linen cupboard and never engages a bolt. Fit and drilling are identical, so a swap between the two needs no drilling.
Run the handle through its full travel before you call it done. The latch should retract with no scraping, and the door should close and stay closed.
HGTV gives a quick trick: mark the latch with bright lipstick, then close the door. The mark on the strike shows you exactly where it hits.
When you swap a slab into an existing frame rather than a whole unit, the hardware work is the same but the frame fit is not. how to install an interior door slab covers what comes first.
Before you buy, know your backset size and your door thickness, and whether you want privacy or passage. With those answers, this is a short job with a screwdriver and a tape measure.
