How to Replace an Interior Door Knob, Step by Step

To replace an interior door knob, measure the door before you order, take the old set out completely, fit the new latch, then the two halves of the new set, then the new strike, and test before you close the door. It takes a screwdriver and, on some sets, a small Allen wrench. My one firm rule is to use every part that comes in the new box, latch and strike included, rather than keeping the old latch to save a few minutes. The answer changes if the door has an old mortise lock, a tall box set into its edge instead of a round hole through its face: that is a different job, covered at the end.

Settle the function and three measurements before ordering

Function first. A passage set has no lock and both knobs always turn, which suits hallways and closets. A privacy set adds a push button or turn on one side, and that side goes in the room being locked, the bathroom or bedroom. A dummy knob is a fixed knob with no latch at all, used on closet doors held by a catch and on the fixed half of a double door. I would buy the function the door needs now, since it is not something you can change by moving parts around later.

Then measure three things with a tape, with the old knob still in place.

Door thickness. Measure across the door edge. Interior doors are commonly 1-3/8 inches thick and exterior doors 1-3/4 inches, but check yours, and check that the set you choose lists your thickness. Emtek's specifications, for one, differ from model to model, so read the range on the exact set.
Backset. Backset, the span between the door's edge and the middle of the round hole, is read across the door's face. The two standard sizes are 2-3/8 inches and 2-3/4 inches, and many latches adjust between them, but confirm the set covers your number.
The holes. The common setup is a 2-1/8-inch hole bored straight through the slab and a 1-inch hole in the edge for the latch. If yours are larger, the new rose has to cover them. Note too the shape of the latch's faceplate: square corners, rounded corners, or no plate at all, just a round collar driven into the hole. Many sets come with more than one faceplate, and matching the recess already cut saves chisel work.

With those in hand, the interior door sets page narrows quickly. Knobs are not handed, so a knob fits a door that swings either way. If you are switching to a lever, check whether the lever you like is reversible or ordered by hand.

Take the old set out, latch and strike too

Work from the side with the screw heads, the room side on a privacy set. If you see two screws on the rose, back them out while holding the far knob, and the two halves pull apart. If you see no screws, look for a small slot in the knob's neck, press the catch inside with a pin, and slide the knob off; the rose cover then comes away to reveal the screws. Some knobs instead have a set screw under the neck, released with an Allen wrench.

With both halves off, remove the two screws in the latch faceplate and slide the latch out of the edge. A latch that has been painted in may need a thin blade run around the faceplate first. Then unscrew the strike from the frame. Before you go further, look at the holes. Clean out splinters and old paint, and check that the edge hole meets the face hole cleanly. A latch that has to be forced in will drag forever.

Fit the new latch with its bevel toward the frame

The latch goes in first, on its own. If it adjusts for backset, set it to the number you measured; the set's instructions show how, and on many latches it is a matter of extending or turning the bolt housing until it locks at the longer size. Slide it into the edge hole with the angled face of the bolt pointing the way the door closes, toward the frame and the stop. Get this backward and the bolt can never catch.

The faceplate should sit flush in its recess, not proud of the edge and not sunk below it. Screw it home. Emtek's sheet for its CF mechanism specifies two #8 by 3/4-inch wood screws for the latch, supplied in the box; use whatever your set provides rather than the old screws, which were sized for different hardware.

This is the step where reusing the old latch tempts people, because it already fits. Resist it. The latch is the part the spindle drives, and the spindle in a new set is made for the latch packed with it. An old latch from another maker may engage poorly or not at all, and the knob ends up turning without fully pulling the bolt back.

Fit the two halves through the latch, then the knobs

How the halves go together depends on the set, and the instruction sheet in the box wins over anything general. On a typical through-bolt set, the outside half carries the spindle and two posts. Pass them through the latch from the outside face, then fit the inside half over them, line up the screw holes and drive the two machine screws evenly, alternating, until the roses sit flat and snug.

Many better-made sets use a different arrangement: a mounting plate or housing screwed to each face of the door, a rosette that threads or locks over it, and a knob that slides onto the spindle and is held by a set screw. Emtek's CF mechanism, for example, has the rosette secured with a ring fastener and a plastic wrench provided, and the knob locked on with a pre-installed set screw and a 3/32-inch Allen wrench. These take a few minutes longer and give you a knob you can snug up later without taking anything apart. On a privacy set, Emtek's sheet for that mechanism also has a privacy pin screwed through the inside trim into the latch, so watch for the step that connects the lock to the bolt.

Before tightening anything fully, turn each knob. The bolt should pull back smoothly and spring out again, and the roses should sit square to the door. If the bolt hesitates, a screw is pulling the halves out of line; ease it off and even them up.

Fit the new strike, then test with the door open

Screw the new strike into the frame, using the old recess if it fits. A strike in the same finish as the knob is one reason to use the one in the box; the other is that its opening is sized for the bolt it came with. If the new plate is a little larger than the old recess, pare the recess with a sharp chisel until the strike sits flush. Plug and redrill old screw holes that sit too close to the new ones.

Test in this order, door open, before you ever close it:

Turn each knob several times; both should return to rest on their own.
On a privacy set, lock it, try the outside knob, then try the emergency release on the outside if the set has one.
Close the door slowly and watch the bolt meet the strike. It should drop in without a shove and hold the door without a rattle.

If the bolt hits the strike plate instead of the opening, the door has dropped on its hinges or the strike is set a little off. Tighten the hinge screws before moving the strike.

The tradeoff of the every-part rule is a little more work: a new strike that needs its recess trimmed, and screw holes to plug. I think it is worth it, because the new set is then a matched system, and nothing in it depends on a part from someone else's design. If you are choosing styles at the same time, the door knobs and door levers pages show the shapes; both fit the same prepared door as long as the measurements match.

If the door has a mortise lock

Older doors sometimes hold a mortise lock: a rectangular case set into a pocket in the door edge, with the knob spindle passing through it and often a keyhole below. A tubular knob set does not fit that pocket. You either replace like for like with mortise hardware made for the existing case, or fill and redrill the door for a bored set, which is a carpentry job as much as a hardware one. My advice is to measure the case and the spindle position before buying anything, and if you are not sure what you have, a photo of the door edge with the old faceplate off answers it.