What you need to do before you start

Replacing an exterior door knob takes about 20 to 30 minutes and requires only a screwdriver and a new knob. The hardest part is not the removal — it is making sure you buy the right replacement. Exterior knobs are not all the same size, and the hole in your door may not match a standard knob you find at a hardware store.

Before you buy anything, measure the distance from the center of the knob hole to the edge of the door. This is called the backset, and it is almost always either 2.375 inches or 2.75 inches. Write this number down. You also need to know whether your door has a deadbolt — a separate lock above or below the knob — because that changes what kind of knob you can install. If the knob itself locks (you turn it to lock), you have a privacy knob, and you can replace it with any knob that has the same backset.

Check the thickness of your door too. Most exterior doors are 1.75 inches thick, but some are thicker. The knob packaging will tell you the range it fits. If your door is thicker than what the knob supports, the mechanism will not work.

Key Takeaways

  • Measure your door's backset (center of knob hole to edge) before buying a replacement — it is either 2.375 or 2.75 inches, and buying the wrong one means the knob will not fit.
  • Remove the interior knob first by unscrewing the set screw on the side, then pull both knobs apart to access the mounting plate.
  • Unscrew the mounting plate from inside the door, slide out the old mechanism, and install the new one by reversing the steps.
  • Test the lock and the door latch before you close the door fully, because some knobs require adjustment to the latch bolt.

How to remove the old knob

Start on the inside of the door. Look for a small hole or a slot on the side of the interior knob — this is the set screw. Push a flathead screwdriver or a small Allen wrench into it and turn counterclockwise. You will feel it loosen. Once it is loose enough, pull the interior knob straight toward you. It will slide off the spindle (the metal rod that runs through the door).

Now look at the base of the knob — the part that sits flat against the door. You will see screws holding a metal plate to the door. These are the mounting screws. Unscrew both of them. The entire mechanism — the plate, the spindle, and the exterior knob — will come free. Pull it out from the outside of the door.

If you cannot find a set screw, your knob may have a push-button release instead. Look for a small button on the interior knob's base and press it while pulling the knob away from the door.

Installing the new knob

Before you install anything, check that the latch bolt (the part that sticks out and catches in the strike plate on the frame) is pointing the right direction. It should angle toward the frame, not away from it. If your new knob comes with a separate latch assembly, install that first by sliding it into the hole in the edge of the door. The curved part of the bolt should face the frame side.

Insert the new spindle through the hole from the outside. The exterior knob should slide onto the spindle. From the inside, slide the interior knob onto the spindle as well. Align the mounting plate so the screw holes line up with the holes in the door, then tighten both mounting screws by hand first. Do not use a power drill — you can strip the holes.

Once the plate is snug, tighten the set screw on the interior knob. Turn it clockwise until it is firm but not so tight that the knob cannot turn. Test the knob by turning it — it should move smoothly without grinding or catching.

Testing the lock before you close the door

This step prevents you from locking yourself out. Turn the interior knob and watch the latch bolt. It should retract smoothly as you turn the knob, and spring back out when you release it. If the bolt does not move, the spindle may not be seated properly — remove the interior knob, check that the spindle is fully inserted, and reinstall.

If you have a keyed exterior knob, insert the key and turn it. The bolt should retract from the outside just as it does from the inside. Lock the knob by turning the key, then try to turn the interior knob — it should not move. Unlock it and try again. The lock and unlock should be smooth and definite.

Close the door gently without latching it. From the outside, try to open it with the key. From the inside, try the knob. Both should work. Only after both directions work should you close the door fully and test the latch.

What to do if the knob does not turn smoothly

If the knob is stiff or grinding, the spindle may be too long or too short for your door thickness. Remove the interior knob and check that the spindle is not bottoming out against the mounting plate. If it is, you may need a spindle extension (a small metal tube that slides onto the spindle to add length). These come in different sizes and are sold separately at hardware stores.

If the latch bolt does not retract when you turn the knob, the spindle may not be connected to the latch mechanism properly. Remove the interior knob and look at where the spindle meets the mechanism inside the door. It should be seated in a slot or hole. If it is not, reseat it and reinstall the knob.

If the bolt retracts but does not spring back out, the latch assembly may be installed backward. Remove the mounting plate and check that the curved part of the bolt faces the frame, not the interior of the door.

Adjusting the strike plate if the door does not close smoothly

Once the knob works, close the door and check the latch. The bolt should slide into the strike plate (the metal bracket on the door frame) without resistance. If the door is hard to close or the bolt does not line up with the hole in the strike plate, the strike plate may need to move.

Loosen the screws on the strike plate but do not remove them. Slide the plate up or down slightly until the bolt aligns with the hole. Tighten the screws. If the bolt still does not fit, the hole in the strike plate may be too small. You can enlarge it slightly with a file, or replace the strike plate with one that has a larger hole.

Frequently Asked Questions

Do I need to remove the door from its hinges?

No. You can replace the knob with the door hanging in the frame. The only time you need to remove the door is if you are replacing the latch assembly and the door is too thick or the hole is in the wrong place — but that is a different job than knob replacement.

What if the backset on my new knob does not match my door?

The knob will not fit properly. The hole will be in the wrong place, and the mounting plate will not sit flat against the door. Return the knob and buy one with the correct backset. Measure twice before you buy.

Can I replace a keyed knob with a privacy knob?

Yes, as long as the backset is the same. A privacy knob locks from the inside only and does not need a key. It is a simpler mechanism and works in the same hole. If you want a keyed lock on the exterior, you need a keyed knob or a separate deadbolt.

Why is my new knob loose even after I tightened the set screw?

The set screw may not be making contact with the spindle. Remove the interior knob and look at the spindle — it should have a flat spot or a groove where the set screw grips. If the spindle is round all the way around, the set screw cannot hold it. You may have the wrong knob for your spindle type.

How tight should the mounting screws be?

Tight enough that the plate does not move, but not so tight that you strip the holes in the door. Hand-tighten first, then use a screwdriver to snug them down. If you hear a cracking sound, stop — you are overtightening and may split the door.