What is depth in measurement?

Outside of the mathematics class, context usually guides our choice of vocabulary: the length of a string, the width of a doorway, the height of a flagpole, the depth of a pool. But in describing rectangles or brick-shaped objects, the choice of vocabulary seems less clear.

Question: Should we label the two dimensions of a rectangle length and width; or width and height; or even length and height? Is there a “correct” use of the terms length, width, height, and depth?

The choice of vocabulary here is entirely about clarity and lack of ambiguity. Mathematics does not prescribe rules about “proper” use of these terms for that context. In mathematics as elsewhere, the purpose of specialized vocabulary is to serve clear, unambiguous communication. In this case, our natural way of talking gives us some guidelines.

Length: If you choose to use the word length, it should refer to the longest dimension of the rectangle. Think of how you would describe the distance along a road: it is the long distance, the length of the road. (The words along, long, and length are all related.) The distance across the road tells how wide the road is from one side to the other. That is the width of the road. (The words wide and width are related, too.)

When a rectangle is drawn “slanted” on the page, like this, it is usually clearest to label the long side “length” and the other side “width,” as if you were labeling a road.

Height: When a rectangle is drawn with horizontal and vertical sides, the word height makes it clear which dimension is meant; height labels how high (how tall) the rectangle is. That makes it easy to indicate the other dimension—how wide the rectangle is from side to side—by using the word width. And if the side-to-side measurement is greater than the height, calling it the length of the rectangle is also acceptable, as it creates no confusion.

Notice that in this case, when height is used, the comparative size doesn’t matter. Because height is always vertical, either measurement, width or height, can be greater.

For some non-rectangular shapes the terms length, height or width would remain unclear, show explicitly what you mean  and refer to it as “this distance” or “this measurement.”

When naming the dimensions of a three-dimensional figure, the only rule is make sense and be clear. It will help to use labels.

When the figure is “level,” height clearly refers to the vertical dimension—how tall the figure is—regardless of whether that dimension is greatest or least or something in between; length (if you use the word) refers to the longer of the other two dimensions. But you may also refer to the other dimensions as width and depth (and these are pretty much interchangeable, depending on what “seems” wide or deep about the figure). See these examples.

When height would be unclear—for example if the figure is not “level” —people cannot know what is meant by width, depth, or height without labels, although length is generally still assumed to refer to the longest measurement on the figure. And, as in two dimensions, terms like “length,” “width,” and “height” won’t feel natural or be clear for some shapes, like a tennis ball.

Commonly abbreviated as D, depth is a measurement of how far back a three-dimensional object is. For example, measurements of an object, such as a computer monitor, are commonly measured as (D x W x H), short for Depth by Width by Height. In the illustration, the Z-axis is the depth.

When we talk about measurement in English, you may find terms you don't know how to use. In this article, we will speak of depth and width and the meaning of each one.

Depth measures the distance between the end and the beginning part of an object; you can use it to determine how profound a pool is. Width measures an object from one side to another; you can use width to determine how broad a door is.

Depth and width seem to be related to mathematics. But don't get confused here; that's not the only use for these words. Let's see more details about them to understand where they come from and the meanings they have.

To understand more about these two terms, we will look into their origin and meaning throughout history.

The term "depth" comes from the proto-germanic word "deupaz," which means sea, valley, and deep. It made it to the English language somewhere in the 14th century; at the time, it was spelled as "dīepþ." By the 15th century, the spelling changed to "depthe."

The term "width" is a combination of the word "wide" and the suffix "th." To know its origins, we need to see the etymology of the word "wide." comes from the proto-germanic word "wīdaz," which means separated in two. It made it to the English language as "wīd" somewhere in the 14th century. Later on, in the 15th century, the spelling changed to "wid." The suffix "th" converts "wide" from an adjective to a noun.

The term "depth" has kept its meaning ever since its origin. Some of the meanings the word has had throughout the time include:

The term "width" has varied its meaning; the Proto-Germanic languages intended it to mean separated into two parts. In Old English, it was a synonym for "far," people used it to refer to long distances. Nowadays, some of the meanings include:

Now that we understand the origin of these words and their meaning, it is time to explain how people use these terms. Depending on the context, words can have different meanings or applications.

You will use the word depth when you talk about objects that are under the ground. Some things that have depth include pools, sea, lakes, wells, pits, etc. Also, drawers, forests, and seasons have depth.

You can find width as an attribute when doing online shopping. It will usually specify the length from side to side, considering you are viewing the front of the object.

There are several mathematical applications where people use the terms width and depth.

As in any other language, in English, you can find symbolic speech. For instance, the word "depth" has a metaphorical meaning. It refers to having intense or severe qualities.

You can say a paint, a book, or even a color has depth. When you use the term to describe something like this, you are not referring to the object's actual size.

The pronunciation of these words is straightforward. Both terms have only one vowel sound.

The IPA symbols we have in "depth" are:

For the word "width," we have:

To pronounce the word "depth," you will start with the tip of your tongue touching your upper teeth while you push air from your throat, release the seal. Slightly open your mouth, relax your tongue and vibrate your vocal cords to make the vowel sound. Close your lips together to make the /p/ sound. To make the final sound, put your tongue as if you were to bite it and push air to make the /θ/ sound.

To pronounce the word "width," start with your lips rounded and almost closed, vibrate your vocal cords. Spread your lips into a relaxed position to make the "i" sound. Your tongue comes into action and will move to cover your palate and stop vibrating your vocal cords. Put your tongue as if you were to bite it and push air to make the /θ/ sound.

Here we have other words that are related to the terms "Depth" and "Width."

Some of the words you can use to substitute "Depth" in a sentence include:

In the figurative speech, you can use the following synonyms:

Some of the words that have a similar meaning to "Width" are:

Here we have some sample questions using the terms "depth" and "width."

The terms "depth" and "width" are both related to measurements. The main difference between them is that depth measures from top to bottom, while width measures from side to side.

There are several uses of these terms. The general usage is a measurement, but you can also find it in mathematics, science, and figurative speech.