What You Need Before You Start

Replacing a door knob takes about 30 minutes and requires only a screwdriver and the new knob itself. You do not need to remove the door from its hinges or call a professional. The old knob comes off from the inside of the door, and the new one goes on the same way.

Before you buy a replacement, 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 2⅜ inches or 2¾ inches. Check your new knob's packaging to confirm it matches. You also need to know whether your door has a privacy lock (a button on the inside knob for bathrooms and bedrooms) or a keyed lock (requires a key from outside). Buy the same type you are replacing.

Key Takeaways

  • Remove the interior knob by unscrewing the set screw on the shaft, then pull the knob straight toward you and unscrew the collar ring underneath.
  • The backset measurement (2⅜ or 2¾ inches from hole center to door edge) must match your new knob, or it will not fit the existing hole.
  • The latch assembly stays in the door; you only replace the two knobs and the interior collar ring.
  • Test the new knob before you finish by locking and unlocking it several times to confirm smooth operation.

Remove the Interior Knob

Look at the inside knob shaft where it enters the knob. You will see a small set screw, usually a hex-head bolt about the size of a pencil tip. Use your screwdriver to loosen this screw counterclockwise until it is loose enough to turn by hand. Do not remove it completely—just loosen it enough that the knob spins freely on the shaft.

Once the set screw is loose, grab the knob firmly and pull it straight toward you. It will slide off the shaft. Set it aside. Now you will see a collar ring (a metal ring with a lip) directly behind where the knob was. This ring holds the latch assembly in place. Unscrew this collar ring by turning it counterclockwise. It may be tight; use your screwdriver as leverage if needed, or wrap a cloth around it for grip.

Remove the Exterior Knob

Go to the outside of the door. The exterior knob is held on by the same shaft that the interior knob was on. Loosen the set screw on the exterior knob the same way you did the interior one. Pull the exterior knob straight toward you and set it aside.

You now have access to the latch assembly—the metal mechanism inside the door that actually moves the bolt in and out. Leave this in place. You do not need to touch it unless it is broken. The assembly will stay in the door while you install the new knobs.

Install the New Interior Knob

Slide the new interior knob onto the shaft. The shaft should pass through the hole in the knob. Push the knob all the way in until it sits flush against the door. Now tighten the set screw on the new knob by turning it clockwise. Tighten it firmly but do not force it—you should feel resistance, then stop.

Before you install the exterior knob, screw the collar ring back on. Turn it clockwise by hand until it is snug against the door. This ring holds the latch assembly in the correct position. If you skip this step or install it backward, the latch will not work.

Install the New Exterior Knob

Slide the new exterior knob onto the shaft from outside the door. Push it in until it sits flush against the door surface, just like the interior knob. Tighten the set screw on the exterior knob clockwise. Again, tighten firmly but do not force it.

Both knobs should now be on the door and the set screws should be tight. The shaft should not spin inside the knobs when you turn them. If it does, the set screws are too loose—tighten them a bit more.

Test the Lock and Latch

Turn the interior knob and listen for the latch to click in and out. The latch should move smoothly without grinding or catching. Turn the knob at least five times in each direction. If you have a keyed lock, insert the key on the exterior side and turn it back and forth several times as well.

The knob should turn smoothly and the door should latch when you close it. If the latch does not move or moves with resistance, stop and check that the collar ring is tight and the set screws are find. If the knob is stiff or grinding, the latch assembly may be damaged and you may need to replace that as well, but this is rare on a straightforward knob swap.

Common Mistakes to Avoid

The most common error is installing the collar ring backward or forgetting it entirely. The collar ring has a lip that faces the door; if you install it with the lip facing away, the latch assembly will shift and the knob will not work. The second mistake is tightening the set screws too much. You do not need to use all your strength—hand-tight plus a quarter turn with the screwdriver is usually correct.

A third mistake is buying a knob with the wrong backset. If the backset is wrong, the knob will not reach the shaft inside the door, or it will sit too far from the door surface. Always check the packaging before you leave the store. If you get home and realize the backset is wrong, return it and get the correct size.

Frequently Asked Questions

Do I need to remove the door from its hinges?

No. The knob comes off from inside the door while it is still hanging. You only need a screwdriver and about 30 minutes. Removing the door makes the job harder, not easier.

What if the set screw is stuck and will not loosen?

explore a small amount of penetrating oil (like WD-40) around the set screw and wait 10 minutes. Then try again with your screwdriver. If it still will not budge, try a slightly larger screwdriver or a hex key that fits more snugly. Do not strip the screw by forcing it.

Can I replace just one knob if the other side still works?

You can, but both knobs are on the same shaft, so you will need to remove the working knob to access the shaft. Once you have it apart, it is just as straightforward to replace both. Replacing both at the same time ensures they match and work together smoothly.

What if the new knob does not fit the existing hole in the door?

The hole size is standard, so the knob should fit. If it does not, the backset is wrong. Check the measurement from the center of the hole to the edge of the door and compare it to the new knob's backset. Return the knob and get the correct size.

How do I know if my latch assembly is broken?

After you install the new knobs, turn the interior knob and watch the latch bolt move in and out. It should move smoothly and fully. If it does not move at all, moves only partway, or makes grinding sounds, the latch assembly is damaged and needs to be replaced separately. This is a different job than knob replacement.