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Standard Size Door Knob Hole (Explained)

A door knob hole also known as a ‘Bore Hole’ is one of the two main components in how a door is prepped. The bore hole is the large main hole through which the door knob mounts. Most doors are prepped with one door knob hole.

It is a common mistake to buy a door knob that does not fit correctly. Taking measurements is very important before you buy a new door knob. Especially if the door is one of the older ones.

But for newer doors, there is a standard size. We will do an in-depth discussion of some commonly asked questions about standard size door knob holes.

Standard size door knob hole

For most modern doors, the standard size for a door knob hole is 2 1/8 inches in diameter. Although, for older doors, the hole size is smaller in general. So, if you want to fit a modern door knob in your old door, you may need to re-drill the door and make a bigger door knob hole.

A door knob is often overlooked but a necessary device. It is a clever mechanism that is practical and at the same time very easy to use. A door knob has a spindle or bolt that runs through it.

It sits right above a cylinder to which the spindle is connected. When we turn the door knob it pulls the cylinder in the direction of the turn. The end of the cylinder is a latch that prevents the door from being opened if the knob is not turned.

We can find door knobs of different shapes and sizes. While picking a door knob, looks are not the only thing that we need to look at. We need to make sure the door knob fits your door perfectly.

That is why it is crucial to know the size of your door knob hole. Without knowing your door knob hole shape you cannot buy a door knob that fits your door.

That is where having a standard shape door knob hole helps. Nowadays, most doors come with a standard size door knob hole.

It makes it easy for the manufacturers to produce door knobs as they do not need to make door knobs for too many different size door knob holes. Besides, it makes it easy for the consumers to replace the door knob when needed as we do not need to measure it then.

However, if you have an older door, your door knob hole may not fit standard size door knob.

You have two options then, either you need to buy a door knob that will fit in a smaller door knob hole or you need to re-drill your door to widen the door knob hole to accommodate a standard size door knob.

Is there a standard door knob size?

Yes, there is a standard size for door knobs. Although, they have varying sizes which is why you need to get the right size that will fit perfectly in your door. Otherwise, your door knob will not function correctly.

Door knobs mainly come in two different shapes. The sizes are 3/8 inches or 2 3/4 inches. These standard knob shapes may fit doors from 1 3/8 inches to 1 3/4 inches thick.

To determine which size of the door knob you will need, you need to make some key measurements. You need to measure the door’s boor hole diameter, backset, and, thickness. That way you will be able to take the right decision when you buy a door knob.

There are also some door knobs that come in adjustable sizes. You can easily change their size to fit them in your specific door size. These adjustable door knobs are rather wonderful as it decreases your hassle and makes thing easier.

Are door knob holes universal?

Door knob holes are not universal but most modern doors have a standard size door knob hole. There are no universally set rules for door knob holes that need to be followed. Although, having a standard size door knob hole definitely helps.

There are many kinds of door knobs available in markets that can fit into different door knob holes.

To have a door knob and deadbolt, two sets of boor holes need to be made.

A door knob hole is often made considering the standard size but there are not any set rules.

For older doors, the door knob hole size is often smaller. Each era had different types

Of door and were made following different customs. In modern times, to make things simple, a standard size is being followed for door knob holes.

But it does not need to be followed explicitly as different sizes of door knobs are still in production. So, it can be said that door knob holes are not universal.

3 factors that determine the door knob hole size:

There are a few factors that influence the door knob hole size and they are rather interesting. Let us discuss these factors that will help us understand why door knob size varies.

Interior door:

Interior doors are the most common doors we see. Interior doors nowadays have a standard door knob hole size.

For interior doors, looks are rather important. That is why interior doors have a focus on how they look and so the door knob hole size gets determined by this factor.

Exterior door:

Unlike interior doors, exterior doors have a strong focus on security. These doors are built around secure they are.

Naturally, the door knob hole size gets influenced by it. For these doors, door knob hole size gets determined by if they can fit door knobs with a good security system.

Door knob latch:

Another very important factor that determines the door knob size is what type of latch your desired door knob has. Various door knobs use different types of latches. Consequently, the door knob hole size heavily relies on this fact also.

How do you measure for a door knob hole?

Measuring the door knob hole is a simple task. To measure a door knob hole, you need a measuring tape and a pencil. Follow our step-by-step guide to measure for a door knob hole:

Remove the current door knob:

Our first step is to remove the current door knob placed on the door knob hole. With the door knob off you can directly see the door knob hole.

This also allows you to have access to the door knob whole so that you can move to the next step of measuring.

Locate the center of the door knob hole:

The first step is to locate the center of the door knob hole. In order to do that, you just have to determine the hole’s widest point. The end-to-end length of the widest point of the hole is the diameter length of the door knob hole.

Take measurements of the door knob hole:

Place your measuring tape firmly across the broadest area of the door knob hole. Starting up to the bottom to the top part of the door knob hole. Be careful to place the measuring tape correctly to avoid any errors.

Check the measuring tape:

Now that you have taken the measurement, look at the measuring tape carefully to check the reading of the measuring tape. This is the diameter length of the door knob hole. Most standard door knob hole size is 2 1/8 inch.

If your measurement reading shows this measurement, your door has the standard size door knob hole. If your measurement reading shows less than this measurement, you have an older door.

Write down the measurement:

The final step is writing down the measurement you have got. Use a pencil to mark the measurement on the door. You can also write down it in a secure place for future reference.

Final Thoughts

Modern doors have a standard door knob hole size of 2 1/8 inches in diameter. Although, not all doors have the standard size door knob hole. Having a door that does not have a standard size door knob hole may prove to be a problem. But it is still very easily fixable if you follow a proper guide.