The Complete Guide of Binocular Sizes

Are you about to buy a new pair of binoculars but have no clue which binocular size is the one for you?

Then this article is for you.

In this guide, we will take you through everything about:

  • Different binocular sizes
  • How do they differ
  • How zoom differs between sizes
  • What sizes are available on the market
  • Which are the best sizes for hiking, tourism, astronomy
  • And much more

Get ready and take out your notebook as we will take you through a close-up on everything that you need to know regarding binocular sizes.

Lets Start With The Basics

Binocular sizes are specified by a set of numbers such as 7×35 or 10×42.  You can find this number right on the center focus wheel.  The first number indicates the magnification. For example, if that number is 7, it means that you are looking at the object seven times closer than if you look with the naked eye.

Pretty simple, right?

Now, the second number in the set refers to the diameter of the objective lens (the lens at the far end of the binoculars) measured in millimeters.

Binocular sizes explained

Once you know what the set of numbers in binoculars mean, let’s get down to what it means when put together.

We already explained what the first number in the set means.  It is easy to see then that the larger the magnification, the better you will see farther away objects.

But think about this: how far away are the objects you are looking at? Are they really that far away to need a 12x magnification, for instance?

We will get back to that shortly.

The second number in the set bears importance for two reasons. The larger the objective lens, the more light the binoculars will be able to capture, hence providing a brighter and clearer viewing experience.

Needless to say, a larger objective lens will take away bigger space in your bag. Is this always practical?

Binocular sizes and uses

Answering to the question above: probably not. But usually, circumstances will dictate what is best for you.

Let’s say that you are going on a safari.

Perhaps the best option here is to carry a pair of binoculars with a compact 4×21 or 4×30 since safari tours you to where animals are in their habitat. You expect animals to come close to you.

Check out this quick guide to help you decide what is the best size for some kind of events:


Suggested sizes

Stadium sports Compacts: 4×21, 8×25 & 10×25  Midsize: 7×35, 10×50 & 12×50
Concerts/Theater Compacts: 4×30, 7×18 & 7×21  Extra wide angle: 5×25 & 8×25
Vacation or Hiking  Most compacts and wide angles 7×35, 8×42, 10×42 & 10×50
Nature and outdoor activities Most standard sizes: 7×35, 7×50, 8×42 & 10×42 Compacts: 8×30 & 10×30
Boating 7×50, 7×42, 8×42 & 10×42
Hunting For general hunting: 7x to 10x power models Distant game or varmint: 12x or 16x
Bird watching Standard: 8×42  Smaller species: 10×42, 10×50 & 12×50
Low light   7×50 (best light-gathering), 8×42, 10×50

But here is the thing:

We cannot simply stop at size. You see, sometimes you are just going on a light vacation and compacts are not that applicable to such travel. On another hand, maybe you are going on this huge hiking journey and you just don’t want to miss any of the beauty around you so you are ready to bring with you the extra volume and weight (and price).

There are some other factors that you should also factor in when deciding what to use and they do not really have much to do with size but we’d feel irresponsible not to even mention them.

For activities such as boating or camping, consider getting yourself a pair with rubber armoring. Water-proof binoculars are actually relevant here.

If you are going to an event where you have to use binoculars for a longer-time period (e.g. safari or going bird watching), you might want to get long eye relief and good close focusing ability for your binoculars.

Speaking of bird-watching, your focus should be on a good magnification since it is the details what you want.  Birds are so pretty when you can see them in detail.

Using compact binoculars is not only an issue of space, but it also has to do with practicality. A hunter on the move, for instance, might need a compact one to avoid the overweight and discomfort.

How do binocular sizes work?

When it comes to a view, what is it that you are looking for?

Think of a mountain several miles away from where you are.  Let’s say 50 miles.  If you are using a 10×60 binoculars, the mountain will look like it is 5 miles away from you. Not close enough, if you ask us.

Fortunately, some binoculars allow a range of magnification (such as 10-30 x 60).  This is incredibly practical as you can get to see a wider range of far-away sightings and, obviously, your binoculars become a more versatile tool. These binoculars usually come with a small lever near your thumb to regulate magnification.

But remember:

When it comes to the objective lens size, remember that the larger they are, the greater the clarity but the bigger the size, which can make them too heavy and bulky for some activities.

A lens size that is twice the size than other quadruples the light gathered. This is particularly important in poor light conditions.

To better understand how binocular sizes work, let’s quickly go over some useful terms.

We will expand on them more later on.


A prism is a sectioned block of glass that reflects light.  They also correct an image so that it does not look inverted.  The prism is important when it comes to size since it folds the path of light, allowing the size of the binoculars to be much smaller than a telescope.

There are two types of prism that are most commonly used today, BAK-4 and BAK-7.  Within these two, the BAK-7 is used in cheaper models due to its low price and the fact that they are made of less dense glass.  BAK-4 are denser and transmit more light and usually come in more complex models.  Binoculars will bring a label with this information.

Field of view

Are you trying to spot that eagle soaring in the skies?

The higher the magnification, the fewer chances you have to spot it.

This is because a higher magnification means a smaller field of view.  The field of view is normally expressed either in degrees or in the number of meters visible within a range of 1000 m.

If you are looking for that elusive sea eagle or deer, you want a wider field of view to spot it.  A narrow field of view means that you will probably have to pan the binoculars more and you will probably miss it.

Do you see now how you need a good balance between magnification and field of view?

Exit pupil size

Exit pupil size refer to the diameter of the beam of light exiting the eyepieces (the part of the binoculars you place on your eyes).

Eye relief

This refers to the amount of mm you can be away from the eyepiece and still get the entire field of view that your binoculars can afford.


Coating is probably the most important factors in setting apart cheaply made binoculars from quality ones.

So, pay attention carefully!

Especially because cheaply made does not mean cheaply sold.

Also, there is a lot of confusion from misinformation regarding this aspect.

Binocular lenses are made of glass, and glass reflects light.  This reflected light is lost and reduces the quality of your view.  To improve the amount of light binoculars gather, they have optical coatings.

To improve effectiveness, coatings must be very thin and must be applied with an equal thickness to a great level of accuracy. This process is not cheap and this is why many manufacturers simply cut corners.

There are at least 8 lenses in binoculars.  Some of them are cemented together but the rest are separated by a thin layer of air that light has to pass through.  You can see here how coatings are important in order to prevent the loss of light that might occur within every glass-to-air-to-glass transition.

Good coatings enhance sharpness and image contrast.  When you try on a pair of binoculars, check out if the image is sharp enough.  A blurry image means that the coating work is not so good.  After that, check on the price tag.

Popular binocular sizes

Here is the thing

Sometimes it is not easy to decide which binocular size is for you and actually the best choice are some of those sizes which are the most popular ones.

Actually, there are some binocular sizes that have become very common.  They are usually versatile and some of them come at an affordable price.

Keep this in mind:

That the most important thing here is the magnification.

A low magnification will not allow you to see objects that are too far away.  More importantly, if you have a good zoom or a very high magnification, you are also reducing the amount of light that enters the binoculars, hence dramatically reducing your field of view.  The image does not have enough room to allow enough light.

The most common magnifications for binoculars are 5x, 7x, 8x, 10x and 12x.  As explained before, a low magnification sacrifices the size of the image.

You are probably thinking: “but greater magnification means better picture!”

If you use a set of binoculars with a magnification greater than 12x, you will need a tripod to steady it since with this magnification, a slight movement of the object will shake the image out of the viewing zone. Now, since we have been talking about being practical, this probably is not a better choice.

These more powerful magnifications are practical when it comes to astronomy viewing in places with low light.

Compact binoculars

When carrying lots of equipment or going through a rough terrain, most people will go for compact binoculars.  Thanks to new technology, these small gadgets are improving in size and weight.  Remember how we hear that today we have more technology in our mobile phones than what it took to send the first man to the moon?  There is probably a bit of a stretch on that remark, but we are actually probably seeing this for binoculars.

The future for best compact binoculars might even make compact sizes the norm. But today, they are still not as popular as their full-size counterparts.

Binocular lens sizes

Let’s delve deeper into lens sizes.

These will ultimately decide the overall size of the binoculars.  We have already mentioned how the larger the objective lens size the brighter and better resolves the images will be.

Binoculars can be thought of as a twin set of refracting telescopes.  The size of the objectives lens is referred to as the aperture.  This light-gathering part of the binoculars works in the same way as a telescope. You may check out our post, Binoculars vs. Telescope.

When it comes to binocular lens size, the choice is clear:  think of what is the activity you will be performing the most.  If your use for binoculars will be astronomy, a larger objectives lens size and even a larger magnification works great. Mountains and celestial bodies are pretty far and very unlikely to move around.

Sizes for binocular cases

The size of your binocular cases is more related to how bulky you want your luggage to feel.

These cases are usually very light but they do increase the volume of the cargo. This is because their purpose is to protect the binoculars and they need to invest space in shock absorbing.

But then you see that this is an important factor in deciding the size of your binoculars.  Normally, if you have made an important investment in binoculars, you want to protect that investment.  So, you definitively have to go for a case.  A good case means one that has an important amount of cushion to absorb shocks more effectively.

Some other cases are made of aluminum, which makes them hard and more cumbersome to carry.  Other materials used to make them include leather or neoprene.  Most cases include a practical strap for a more comfortable carrying.  In other cases, they are built for a specific type and size of binoculars.

Binocular exit pupil sizes

The exit pupil diameter has to do with the brightness that your binoculars provide.

It refers to the diameter of the ray of light that will hit your eye’s pupil after it has traveled through your binoculars.

To determine this diameter, all you need to do is divide the diameter of the objectives lens with the magnification.  For instance, a 10 x 60 binoculars will have an exit pupil size of 60/10 = 6 mm.

But how important is this?

During daytime, your pupils will contract to a size of 2-4 mm.  However, at night, they will expand to 7 mm.

You can see how the objectives lens sizes and magnification ratio here is important.  If the exit pupil size of your binoculars is wider than the size of your pupil all of the light will not get through.  So, during the daylight, binoculars with a 4 mm exit pupil size will look just as bright as those with 6 mm.

But during the night, when your pupils are expanded, the 4 mm exit pupil size will not be as bright as the 6 mm one.  As we get older, our pupils tend to decrease in diameter.  So, a person in their early 60s probably expands their pupils to only 5 mm.  Large exit pupil sizes do not really offer much of an advantage.

Conclusion: Larger exit pupil sizes make no difference during the daylight, but they are a charm in conditions of low light when pupils are dilated to their maximum.

Astronomy binocular viewing recommended sizes

Let’s look at this.

Many stargazers prefer to use binoculars over telescope to look at celestial bodies.  This is mainly because they offer a much wider field of view than telescopes.

Speaking of Field of View, you have probably read that a particular set of binoculars offer a Field of View of 298ft at 1000yds or 5.7 degrees, which is the same thing.

If you were not raised on a boat or a spaceship, those numbers will probably be unfamiliar to you.  If you are only given the degrees, simply multiply those degrees times 52 feet and that will give you the field of view at 1000 yards.

Still no idea of what a degree looks like? The disk of the moon has a width of 1/2 degree.

For stargazing, the best binocular sizes are those that offer the largest magnifications.  So, don’t be afraid to pick a 12×70, 25×70, or a 25×100 for that.  You will place it on a tripod for stability anyway, so you should be fine.

You may also like: Using Binoculars for an Eclipse

20×50 binocular sizes

The 20×50 binoculars sizes are very practical to carry on a backpack or hanging on your neck.  But do know that these are not compact sizes necessarily and they will take some extra space in your bag.

This binocular size is actually pretty good to give a closer look at the moon and Jupiter.  These are big and will wobble a lot so it is best to put them on a tripod.  They are not too useful when it comes to outdoor activities.

Binocular sizes 10 x 40

Let us take a quick look at one of the most popular binocular sizes out there.

As you already know, the 40 means that the diameter of the objective lens is rather compact, which is great.  The magnification is perfect for most adventures that you might find yourself in.

This is perhaps the most popular binocular size used for pretty much any outdoor adventure.  It is easy to carry and will be all you will need during your travels, either to a mountain or around the world.  They are still rather heavy and you might get tired from carrying them.

Small binocular sizes

Don’t let the size of the binoculars fools you.

More powerful binoculars are not always the best as we have said over and over; it will all depend on the activities you are most engaged on.  Many times, it is more important to be practical and smaller sizes will make your experience as good.

Once again, you should place all factor on the balance and decide what is best for you.

If you are hiking or backpacking, your equipment needs to be lightweight, durable, and capable of overcoming the challenges of weather.

As with durability, small binocular sizes can come with a fiberglass reinforced body, multi-coated lenses to repel fog and water, all in an 8×25.  Sometimes, more powerful is less.

Standard binocular sizes

There truly is no standard when it comes to binocular sizes.

However, having a practical, comfortable, small-sized and powerful binoculars is the aim for the future.  To create a binocular that as good to watch a mountain as it is to observe Jupiter.

In the case of binoculars, probably size does matter.  It would be nice if you could carry lightweight binoculars with the power of a 20×50, or a 20×60 in a very small size.

If you want to know what the best binoculars under 200 or under 100 review click the link.

Some people might even venture to say that the standard binocular size is up to you. The best one is the one you have with you, is what they’d claim.

Since we are trying to have you make an educated decision BEFORE you venture for your new pair of binoculars, we will go ahead and say that the standard for you will be what you get next.

Nevertheless, we can say that the majority of the population that gets themselves a brand new pair of binoculars, they will usually go with a 10×40 mm.  There are plenty of brands out there that will offer the specifications you require or advise you on a better choice.  After this article, we are sure you can now go and flash some sage wisdom at the store and point at what it is specifically that you want.


You might be buying the wrong pair of binoculars!

After reading everything you need to know about size, magnification, field of view, exit pupil, etc., you should get the best item for you.  Make your purchase based on what will work best.

Perhaps you need a large field of view for your hunting party, but then you are not willing to make the purchase or have to carry around a heavy and bulky piece, adding to your already heavy load.

You have been proven that there is more to binoculars than two simple telescopes mashed together. You can now be an expert and when it comes to binocular size, make a great call.

Good luck!

You may also like: Understanding Binoculars

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