What Do the Numbers on Binoculars Mean? Complete Guide 2023

By Richard

The important question that a seller asks is what configuration of binoculars you need. How will you answer if you don’t know what do the numbers on binoculars mean?

It is very important to know the number that explains the functionality and specification of binoculars. Only those who used binoculars at some stage of their lives know the meanings of numbers present on binoculars.  In this guide, we will provide you with in-depth knowledge about numbers and specifications present or written on the binoculars.

The brief model number written on the box of binoculars mainly represents magnification and objective lenses. The first number before X is used to display the magnification strength whereas the second number that comes after X represents the diameter of the objective lens. For example, in 10X42 binoculars 10 is magnification power and 42 is the diameter of the objective lens which is measured in millimeters.

This question needs an answer in detail so let’s dive deeper to get in-depth details about the number and specification of binoculars.

Related article: 10X50 vs 20X50 Binoculars

Basic Knowledge About What the Number and Specification of Binoculars Mean

Before going deeper and understanding the specification and numbers o of binoculars, it is important to get the basic knowledge of numbers that are very important in showcasing the specifications of binoculars.

The main specification of binoculars depends on two numbers separated by X. For example 10X42 binoculars. 10 represents the power of magnification which means how magnified an image binoculars give to the users. The bigger the magnification number, the more magnified images will be shown to the users.

The magnification differnce between 8x and 10x binoculars
The magnification difference between 8x and 10x binoculars

The picture given above shows the comparison of two magnification powers (8x and 10x). The elephant appears less amplified with 8x magnification than at 10x magnification.

Objective Lens

The second number in the specification represents the diameter of the objective lens. It is usually measured in millimeters and is considered a vital part of binoculars. The major function of objective lenses is to capture the light and show a brighter image. Different sizes of objective lenses are available in the market. 

Size of objective lens - how to understand the numbers on binoculars
Size of objective lens – how to understand the numbers on binoculars

Is it good to have a bigger objective lens?

Some newbies after reading reviews make up their minds that the binoculars with bigger objective lenses will give more quality images and hence they buy the binoculars with 50 mm of objective lens diameter.

It is totally a wrong practice as increasing the size of the objective lens increases the weight of binoculars. The optics with a greater diameter of the objective lens are bulkier than the binoculars with less size of the objective lens. 

It is worth noting that binoculars with less weight are more useful as they don’t make you tired. Choosing the normal diameter of an objective lens like 42 mm is more than enough to give a nice image. This size of the objective lens won’t make them heavyweight as well.

What is the ideal magnification for outdoor activities?

It is another simple yet technical question that makes people confused. Many magnification powers are available in the market. But keep in mind that every magnification strength is used for a specific outdoor activity.  

Choosing 12x magnification for hunting is useless. Similarly, the 5x magnification will never work fine in birding. In hunting, you need less magnification and a greater field of view. But in birding, the field of view is not the point to talk about and everything is concerned with magnification power.

8x magnification is best for hunting as it gives an ideal field of view. At the same time, 12x magnification is good for birding as it gives a fully magnified image to observe every minute detail of the targeted object. 

For stargazing or astronomy, even high-powered magnification is needed as you will be seeing objects that are very far away from you. 

 A simple formula to remember magnification strength is given below

  • 8x will give you eight times bigger size of the targeted object
  • 10x will give a ten times bigger image than the actual size
  • 15x will give you fifteen-time bigger image than the actual size

Keep relating now by using the above formula of knowing what binocular strength means in binoculars.

Binocular Specifications and Numbers Explained, With Tips on Understanding Them

Not only magnification and objective lenses but there are many other numbers that need an explanation to complete the answer to the question What do the numbers on binoculars mean?

Infographics explaining what do numbers on binoculars mean
Infographics explaining what numbers on binoculars mean

Understanding the numbers which describe the binoculars is very important. Apart from magnification and objective lens, the following numbers and factors are key in understanding binoculars.

  • Number Explaining Field of View
  • Number Explaining Close Focus
  • Number Explaining Eye Relief
  • Number Explaining Exit Pupil
  • Number Explaining Interpupillary Distance

The binoculars buying guide without mentioning any of the above elements is literally incomplete. We will dive deeper to understand more about choosing binoculars and all those numbers which are used to explain the specification of binoculars.

1- Field of view

Field of view (FOV) is defined as how much area a person can see with binoculars without moving them. The field of view is very important to consider when buying binoculars for hunting and other outdoor adventures.

Field of view requirement is different in different outdoor activities. For instance, you need a greater field of view for hunting but need a lesser field of view for birding or stargazing.

Relationship of magnification power and field of view:

The binocular with greater magnification power has less area to view, search or locate the target. Both are inversely proportional to each other.

Magnification ∝ 1/field of view

The relation given says that if you increase the magnification power then you will have to compromise the field of view of binoculars. This is why, we said earlier, always choose less magnification for hunting. During stalking, you need to locate. The greater field of view definitely helps in searching for the buck by providing a larger area.

Relation between magnification power and field of view

The image shows that the binoculars with less magnification give more area. It becomes easier to locate the target. In contrast, the binoculars with higher magnification power give less area to locate the targeted object. 

Binoculars with a greater field of view

As said earlier, there are two possibilities. If you opt for a larger field of view, you will be able to cover a larger area. But if you find a target in that area, you won’t focus on that target. 

Binoculars with a short field of view

Maybe you’re one of those who love a closer and fully focused look at the target. If yes! Go with binoculars with a shorter field of view. Choosing this type of binocular will reduce your area but increase the focus on the target.

What is the best FOV for a hunter?

New hunters don’t get it easy to find the target. Increased area of lookup will help them to find the target. Ultra-high focus on the target doesn’t help. The most important part of hunting is to find the target. If you fail to find the buck, the alone focus is useless. So binoculars with larger FOV are preferable over shorter FOV. I recommend you choose binoculars with a field of view greater than 350 feet.

2- Number Explaining Exit Pupil Number

Exit pupil is another important point to discuss to give an in-depth answer to the question: What do the numbers on binoculars mean? Every binoculars have a small circle shape white-colored spot on the center of the eyepiece. This small circle is called the exit pupil which represents the size of the beam of light that leaves the eyepiece. It is measured in millimeters. Acknowledging the importance of the exit pupil helps in knowing how to understand binocular numbers.

How to calculate the exit pupil number?

The exit pupil size is calculated by dividing the diameter of the objective lens by the magnification power. Suppose the binocular with 10x magnification power and 50 mm objective lens diameter. Then the size of the exit pupil will be around 5 mm.


The formula to calculate the exit pupil is given below;

Exit pupil = Diameter of objective lens/ Magnification power.

The exit pupil of 10X50 binoculars will be calculated as follows

Exit pupil = 50/10 = 5 mm

Other examples are also given below;

  • The exit pupil of 10X42 binoculars is 4.2 mm
  • 8X42 binoculars have an exit pupil of 5.25 mm
  • The exit pupil of 10X32 binoculars is 3.2 mm

 Ideal pupil number:

The exit pupil of around 5 mm is considered the best size. Anything above 2.5 mm falls under the decent exit pupil size category. If the binocular has an exit pupil of 2.5 mm or less than that, then never buy that binocular as it won’t give enough brighter and clearer images.

3- Number Explaining Close Focus

Close focus is simplified as the closest distance that can be focused with optical instruments like binoculars or scopes. Smaller close focus helps in observing all the minute details of binoculars as it can focus the closer objects. It is especially important in bird-watching binoculars. 

Usually, binocular users don’t bother about close focus during purchasing binoculars. After purchase, they use it to see the closer object and the binoculars fail to give a clear and magnified image of that object. The customers start abusing the sellers. 

In reality, each binocular has its own close focus, which means that each binocular has its own potential to focus on a nearby object. Suppose a binocular has a close focus of 2 feet it means it can only focus on an object which is 20 feet away from it. But it won’t focus on objects which are 19 feet away. 

For stargazing or sightseeing, the close focus of 30 feet is fine as long as you use binoculars far away from the targeted object. But in bird watching, you must have a close focus of at least 10 feet.

4- Eye Relief

Binoculars’ eye relief is a very important factor that tells us how comfortable binoculars will be! For example, those binos that have longer eye relief offer a more comfortable viewing experience as compared to those binoculars that come with shorter or smaller eye relief.

I have already written a complete guide on eye relief. However, let me explain it briefly. Actually, it is the distance between the human eyes and the ocular lenses of the binoculars. When you use binoculars, then there remains the distance between your eyes and the lens, and this distance or space is called eye relief.

It is a very important number for those people who wear glasses due to weak vision. Look, when you wear glasses and use binoculars, then the distance between your eyes and the ocular lens gets increased due to the glasses. Glasses occupy space which reduces eye relief and causes an uncomfortable viewing experience.

But the question arises what is suitable eye relief? Eye relief of 15 mm is considered decent. But I believe that those binoculars that have 15 mm are not ideal for those who wear glasses. So, I recommend everyone choose binoculars having eye relief greater than 15mm. Anything above 17 mm is considered ideal.

5- Interpupillary Distance Distance

Interpupillary Distance (IPD) is a very important thing that you should always consider buying binoculars. There are some numbers that explain IPD. Don’t you know what Interpupillary Distance Actually is?  This number is the measurement between the centers of the pupils of your eyes and is crucial for achieving clear and comfortable images when using binoculars.

The IPD is usually measured in millimeters and can be adjusted on most binoculars to match the distance between your eyes. This adjustment is crucial because if the distance is too wide or too narrow, you’ll experience discomfort, eye strain, and even double vision.

Keep in mind that the IPD varies from person to person, and the average range for adults is between 55 and 75 millimeters. Children have smaller IPD measurements, usually between 42 and 54 millimeters. Therefore, it’s important to consider the IPD range of the binoculars you’re purchasing to ensure that they’re suitable for your eyes.

I recommend you choose binoculars having an IPD ranging between 55 mm to 75 mm. However, if you’re buying binoculars for a child, you can go with a smaller IPD distance that perfectly aligns with the face size of the child. It can be adjusted according to the shape of the person so you don’t need to pay special heed.

Video Explaining What the Numbers on Binoculars Mean


In this article on how to read binocular numbers, all the important numbers and specifications have been explained completely. After reading this, you will be able to go to the optical store and buy a nice pair of binoculars on your own. Keep in mind one wrong decision at any step can bring unsuitable binoculars for you. 

Remember that high pricing doesn’t mean very good binoculars. Similarly, low-priced binoculars are not always bad. Don’t go for the cheapest binoculars as you won’t get any results at all. A mid-range binocular can perform very well in the field.

“Never rush for expensive, nor for too cheap.”

We have listed all those factors. In fact, every factor is explained to help you understand the numbers written on binoculars binoculars

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