You can change a door lock yourself in about an hour with basic tools

Changing a door lock is a straightforward task that most homeowners can do without calling a locksmith. You remove the old lock from the outside of the door, take out the interior hardware, and install the new lock in its place. The whole job takes about 30 minutes to an hour, costs between $15 and $50 for the new lock, and requires only a screwdriver and possibly a drill.

This guide covers the most common residential lock: a keyed entry knob on an exterior door. Interior locks and deadbolts follow the same basic steps. If your door has a mortise lock (an older style where the lock body sits inside a pocket cut into the door edge), the process is different and you should consult the lock manufacturer's instructions or hire a professional.

Key Takeaways

  • Most entry knobs unscrew from inside the door and slide out without tools, making removal the easiest part of the job.
  • You need to know your door's backset — the distance from the edge of the door to the center of the knob hole — before buying a replacement lock.
  • New locks come with installation instructions specific to that model, and following them exactly prevents binding and misalignment.
  • Test the lock from both sides before closing the door to make sure it turns smoothly and the bolt retracts fully.

Measure your door's backset before buying a new lock

The backset is the distance from the edge of the door to the center of the knob hole. Most residential doors use a 2 3/8-inch backset, but some older homes have 2 3/4-inch doors. Buying the wrong backset means the new lock won't fit the existing hole, and you'll have to drill a new one.

To measure, close the door and measure from the inside edge of the door to the center of the knob hole. Write this number down and bring it with you when you buy the replacement lock. If you're unsure, take a photo of the measurement and show it to the hardware store staff — they see this measurement every day and can confirm you have the right size.

Remove the old lock from the inside of the door

Open the door and look at the interior side of the knob. You'll see a small slot or a setscrew on the knob shaft. If there's a slot, insert a flathead screwdriver and turn it counterclockwise until the knob comes loose. If there's a setscrew, use an Allen wrench or screwdriver to loosen it, then unscrew the knob by hand.

Once the knob is off, you'll see the lock body — a metal piece that slides through the door. Push it out from the outside, or pull it from the inside. The exterior knob and lock body will come out together. Set them aside. Some locks have a small metal plate (called a rose) around the base; unscrew it if it's in your way, but you don't have to remove it to take out the lock.

Install the new lock following the manufacturer's instructions

New locks come with specific installation steps printed on the packaging or in a small instruction sheet. Read these before you start. The basic sequence is: insert the lock body through the hole from the outside, position the interior hardware on the inside, and screw the knob on. The exact order and tightness matter — if you tighten the screws too much, the lock will bind and the key won't turn.

Start by inserting the exterior knob and lock body through the hole from outside the door. From inside, slide the interior hardware onto the lock shaft. Hand-tighten the setscrew or slot just enough so the knob doesn't spin freely, then test the lock before you fully tighten it. If the key turns smoothly and the bolt retracts all the way, tighten the setscrew the rest of the way. If it binds, back off slightly and test again.

Test the lock from both sides before you close the door

Before you shut the door, turn the key from the outside and watch the bolt move in and out. Then go inside and turn the interior knob to make sure the bolt retracts completely. The bolt should slide in and out without resistance, and the door should close smoothly without the bolt catching on the frame.

If the bolt doesn't retract all the way, the lock is too tight. Loosen the setscrew a quarter turn and test again. If the knob spins without moving the bolt, the setscrew is too loose. Tighten it a quarter turn and test. This back-and-forth usually takes only a minute or two, and it's much easier to fix now than after you've closed the door and locked yourself out.

Reinstall the interior rose and escutcheon if your lock has them

Some locks come with a decorative metal plate (rose) or a larger trim ring (escutcheon) that covers the hole in the door. If your old lock had one and your new lock does too, slide it over the interior knob shaft and screw it to the door. Make sure it sits flat against the door and doesn't interfere with the knob's movement.

If your new lock doesn't come with these pieces but your old one did, you can usually reuse the old ones. They're just trim and don't affect how the lock works. Slide the old rose over the new lock shaft and screw it down the same way.

Rekey the lock if you want to use your old key

Most new locks come with two keys and a small tool for rekeying. If you want to use a key you already have instead of the new keys that came with the lock, you can rekey it yourself. The instructions come in the lock package and usually involve removing a small plug from the lock cylinder, inserting a special tool, and swapping out the internal pins.

Rekeying takes about 10 minutes if you follow the instructions carefully. If you make a mistake, you can usually undo it and try again — the pins are small but they don't break easily. If rekeying feels too fiddly, a locksmith can do it for $15 to $30, which is much cheaper than buying a new lock just to match your existing key.

Frequently Asked Questions

What if the new lock doesn't fit the hole in my door?

The hole is probably the wrong backset. Measure again to confirm, then buy a lock with the correct backset. If you need a different backset, you'll have to drill a new hole and fill the old one with wood filler. A locksmith can do this in 15 minutes if you'd rather not drill.

Can I change a lock on a rental property?

Check your lease and local tenant laws first. Many places require landlord permission before you change any locks. If you're allowed to change it, keep the old lock and hardware so you can reinstall it when you move out.

What if the key won't turn after I install the new lock?

The lock is too tight. Loosen the setscrew a quarter turn at a time and test the key until it turns smoothly. If loosening doesn't help, the lock body may be misaligned — remove it and reinstall it, making sure it sits flush against the door.

Do I need to replace the deadbolt too?

Not necessarily. Entry knobs and deadbolts are separate locks. You can change just the knob, just the deadbolt, or both. If you change only one, you'll have two different keys, so most people change both at the same time to keep one key for the door.

What if I lose the keys that came with the new lock?

You can rekey the lock to a key you do have, or a locksmith can make new keys from the lock cylinder. Locksmiths charge $5 to $15 per key, which is cheaper than replacing the entire lock.