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What Is The Standard Door Knob Hole Size

door lock hole size
Last Updated on January 22, 2023
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Changing an existing doorknob or fitting a new one is pretty straightforward as it is usually a case of taking the old one out and putting in a new one. But, as with most things, there may be a complication, and, in this case, that could be the doorknob hole size.

The standard door knob hole size is 2 1/8” in diameter and will be that for most modern doors. The doorknob hole is usually smaller for older doors, so if you fit a modern doorknob to an older door, you may need to rebore the doorknob hole to fit correctly.

It’s also important that you know how to accurately measure the doorknob hole size, as well as the door thickness and backset, so you can mark, drill, and fit the new doorknob and backset easily and without pulling your hair out, so let’s establish how to do all that!

How To Measure The Doorknob Hole

Measuring the doorknob hole is another relatively simple task. With the doorknob off, you can see the doorknob hole, and you need to measure its diameter to get an accurate measurement.

Find the widest point on the doorknob hole, which is usually right across the center; take your measuring tape, place it on either end and then read the measurement. Most standard doorknob holes are 2 1/8” in diameter.

If this is the reading you get, you are dealing with a typical, standard doorknob hole; if it’s smaller than that, then the chances are you have an older door and will have to resize the doorknob hole.

There are two other elements you need to measure: the door thickness and the backset.

Why Is Door Thickness Important When Placing A Doorknob?

Checking the door thickness before installing the doorknob will ensure that you don’t need special hardware to fit your doorknob. If the door is standard, the doorknob will slot in just fine.

Although it may seem a menial task, having a fight with your door or having to modify it because you didn’t check the thickness before buying it will be best avoided, so measure first and be sure.

How To Measure The Door’s Thickness

Nowadays, standard doors would be between 1 3/4 “ and 1 3/8” and can be as much as 2” thick. Most door frames are designed to accommodate doors of this thickness, and measuring this is also pretty easy.

While it’s unlikely that your door frame would take a thicker or thinner door, it’s generally a more favorable idea to be safe rather than sorry, so before you buy a door, best measure it first to make sure it’s the correct thickness for the door frame.

Using your measuring tape, place one end at one edge of the door and then extend the tape measure to the other end to read the thickness. Use the tape marking on the very edge of each side to get the most precise thickness measurement.

What Is The Backset And Why Is It Important

The backset is the distance between the face of the lock and the center of the keyhole. This lock face is the part that engages with the door frame to lock the door, and having the proper measurement to the keyhole center means you can align a new lock without having to drill new holes.

How To Measure The Backset

Using your tape measure, measure the bore’s diameter and find the center. The typical distance is between 2 ¾ and 2  3/8. The backset is the distance between the middle of the bore or the doorknob hole to the edge of the door.

You can do this by making a small mark on the door where the middle point is and then aligning the tape measure with that point and pulling it to the door’s edge – this will give you the most precise measurement of the backset.

With building supplies like doors and locksets having standard dimensions, adding a new lock and doorknob is quick and usually easy, and all it takes is removing the old doorknob and lockset and replacing it with a new one.

Are Doorknob Sizes Universal?

Most modern doorknobs will fit most standard doors, but this is not a universal law, so doorknobs are not universal, so you will need to measure the borehole, backset, and door thickness before you install your doorknob.

The fit between the doorknob and the door will depend on the door itself, as older doors will have different doorknob sizes than newer ones. You may also find that indoor and outdoor doors may have different doorknob sizes.

Of course, there are many doorknob designs available, but the internal characteristics will determine whether the doorknob will fit the door, not its exterior looks.

Doorknobs Vs. Door Handles

Doorknobs and door handle perform the same function, and this is to give you a point of contact and leverage to open and close the door and lock it. The leverage and design of each are different, but doorknobs often have variants designed for rim locks, making them more compatible with older doors.

Due to its design, the leverage isn’t a factor with door handles, but doorknobs should be mounted a little back from the door surface to prevent the knuckles from scraping or brushing the door when opening and closing it.

Whether you opt for doorknobs or handles will depend on what type of look at feel you want, but now you know how to ensure your doorknob fits properly.


Adding and installing a new doorknob on an old door or an old doorknob to a new door should be hassle-free, provided you have the right tools like your tape measure to take some basic measurements like the borehole diameter backset and door thickness.

While you can choose the type, design, and material of the doorknob itself, knowing that it will fit into your door of choice before buying it makes that process much less stressful and leave your new doorknob and door looking and working great!

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