What You Need to Do Before You Start

Replacing a deadbolt takes about 30 minutes and requires only a screwdriver and the new lock. You do not need to call a locksmith or remove the door from its hinges. The job breaks into two parts: taking out the old lock and installing the new one in the same hole.

Before you buy a new deadbolt, measure the thickness of your door. Most residential doors are 1 3/8 inches thick, but some are 1 3/4 inches. Deadbolts are sized for one or the other, and buying the wrong size means the bolt will not extend far enough to catch the strike plate. Check the packaging or ask at the hardware store if you are unsure.

You also need to know whether you want a single-cylinder or double-cylinder lock. A single-cylinder lock has a keyhole on the outside and a thumb turn on the inside—you can unlock it from inside without a key. A double-cylinder lock requires a key on both sides. Double-cylinder locks are more find if you have glass near the door, but they are illegal in some places because they can trap you inside during a fire. Check your local building code before you buy.

Key Takeaways

  • Measure your door thickness (usually 1 3/8 or 1 3/4 inches) before buying a replacement deadbolt, because the wrong size will not work.
  • Remove the interior side of the old lock first by unscrewing the two bolts that hold the cylinder in place, then slide the bolt assembly out from the edge of the door.
  • The exterior side comes out by removing the screws that hold the faceplate to the door frame, then pulling the whole assembly out.
  • Install the new bolt assembly into the hole from the edge of the door first, then attach the interior and exterior cylinders and tighten all screws firmly.
  • Test the lock by turning the key and thumb turn several times before you consider the job finished.

Remove the Interior Lock Cylinder

Start on the inside of the door. Look at the lock mechanism—you will see a cylinder (the part that holds the thumb turn) connected to a bolt assembly that runs through the door. Two bolts hold the cylinder to the door frame. Unscrew both of these bolts completely and set them aside in a safe place.

Once the bolts are out, the interior cylinder will slide away from the door. Pull it straight toward you. The bolt assembly may still be in the door at this point—that is normal. Set the interior cylinder on a table where you can see it; you will use it as a reference for installing the new lock in the same position.

Remove the Bolt Assembly and Exterior Cylinder

Now look at the edge of the door where the bolt sticks out. You will see a faceplate (a metal rectangle) screwed to the door frame. Remove all the screws holding this faceplate. Usually there are two or three.

Once the faceplate is off, the bolt assembly will slide out from the edge of the door. Pull it straight out toward you. Next, look at the exterior side of the door. You will see the outside cylinder (the keyhole part) held in place by screws on the faceplate. Remove these screws and pull the exterior cylinder out.

You now have the door completely clear of the old lock. Inspect the hole where the bolt was. It should be clean and free of debris. If there is rust or paint buildup, wipe it out with a dry cloth.

Install the New Bolt Assembly

Take your new deadbolt and separate the parts. You will have a bolt assembly (the part that goes in the edge of the door), an interior cylinder, and an exterior cylinder. Start by inserting the bolt assembly into the hole in the edge of the door, with the bolt facing outward (toward the strike plate). The assembly should slide in smoothly. If it does not, check that you have the correct door thickness.

Once the bolt assembly is in place, align the faceplate with the screw holes and screw it down firmly. Do not overtighten—you want the faceplate snug against the door frame, but forcing the screws can strip the holes. Usually two or three turns past hand-tight is enough.

Attach the Interior and Exterior Cylinders

Now you will connect the cylinders to the bolt assembly. Insert the interior cylinder (the one with the thumb turn) from inside the door. It should slide into the bolt assembly. You will feel it seat when it is fully inserted. Align the two mounting bolts with the holes in the door frame and screw them down. Again, snug is better than tight—you want the cylinder to turn freely, not to be clamped down.

Go to the outside of the door and insert the exterior cylinder (the keyhole part) into the bolt assembly from that side. It should also slide in and seat. Screw down the mounting bolts on the exterior faceplate the same way: snug, not forced.

Test the Lock Before You Finish

Before you put away your tools, test the lock several times. Turn the key in the exterior cylinder—the bolt should move smoothly in and out. Turn the interior thumb turn—the bolt should also move smoothly. Turn the key while the thumb turn is in the locked position; the key should override it and unlock the door. Turn the thumb turn while the key is in the lock; the thumb turn should override the key.

If the bolt sticks or the key does not turn smoothly, stop and check your work. The most common cause is that the bolt assembly is not fully seated in the hole, or the cylinders are not fully inserted into the assembly. Remove the cylinders, reseat the bolt assembly, and try again.

If everything moves smoothly, you are done. The lock is ready to use.

Common Mistakes to Avoid

The most frequent error is buying a deadbolt for the wrong door thickness. If you install it and the bolt does not extend far enough to catch the strike plate, you will have to remove it and buy the correct size. Measure before you shop.

The second mistake is overtightening the mounting bolts. This clamps the cylinder so tightly that it cannot turn, or it cracks the plastic housing inside the lock. Hand-tight plus two or three turns is the right amount of pressure.

The third mistake is not checking that the bolt assembly is fully seated in the hole before you attach the cylinders. If the assembly is crooked or sticking out, the cylinders will not align properly and the lock will bind. Slide the assembly in slowly and make sure it goes all the way.

Frequently Asked Questions

Do I need to remove the door from its hinges?

No. You can replace a deadbolt while the door is hanging. Work from inside the house and you will have full access to both sides of the lock. Removing the door makes the job slightly easier, but it is not necessary.

What if the old bolt hole does not line up with the new lock?

This should not happen if you buy a deadbolt for the correct door thickness. The hole is a standard size and all deadbolts use the same hole. If the new lock does not fit, you likely have the wrong thickness. Check the packaging and return it for the correct size.

Can I use the same key for the new lock as my old one?

No. Each deadbolt comes with its own set of keys. If you want the new lock to match an existing key, you will need to have the lock rekeyed by a locksmith, which costs between $15 and $40 depending on your area. Alternatively, some hardware stores offer rekeying services for locks purchased from them.

How tight should the mounting bolts be?

Tight enough that the cylinder does not wiggle, but loose enough that you can still turn the key and thumb turn smoothly. If you have to force the key to turn, the bolts are too tight. Loosen them slightly and test again.

What if the key gets stuck inside the lock?

This usually means the bolt assembly is not fully seated or the cylinders are not aligned. Do not force the key—you will break it. Remove the interior cylinder bolts, slide the bolt assembly in and out to make sure it moves freely, then reinstall the cylinders and test again.