What Do the Numbers on Binoculars Mean?

If you’re familiar with binoculars, you’ll know that they’re all about numbers. All of their features and options are calibrated in digits, which can be quite overwhelming. You’ll frequently be confronted with the question of ‘’what do the numbers on binoculars mean?’’ 

That is exactly why we’re here today. We’ll walk you through each number, what it relates to, and its effect on the image you’ll see. That way, when you see a pair of binoculars, you’ll know exactly what it can and can’t do.

Just keep in mind that new models are emerging every day, so you might find more advanced models than the examples we’re going to speak of today. Nonetheless, you’ll still know what the number relates to just by its shape. Whether it’s in the hundreds, thousands, tens, or decimals, all these are signs that will guide you.


When a number is multiplied by another, it’s usually related to the calibration of both the magnification power and the objective lens’s diameter. These two numbers can vary greatly, and they have such a significant impact on the image you’re going to see.

Magnification Power

Magnification power means how close you’ll see the object that’s far away from you. This number can range anywhere between 7x and 30x. Additionally, some binoculars come with zoom magnification, meaning that you can control the extent of magnification that you use at different times and situations.

Objective Lens

An objective lens is the lens that you see through, and there are many different types of it, including plastic ones, eco-friendly ones, and extra distention ones. The second number relates to its diameter, and as that gets bigger, the image will be clearer and sharper as more light will come into the binoculars.

1000 Yards

Any number written in yards or feet relates to the field of view. This means how many yards you’ll see through your binoculars, and that’s inversely related to magnification power. Consequently, as magnification goes up, the field of view will go down, as you’ll be focusing on one object rather than the entire scene.


This number with decimals means the available angle of view, which is, in a way, related to the field of view. However, it’s measured in degrees. So, it tells you how many degrees you’ll be able to see through your binoculars in relation to the 360° present around you.

BAK4, BK7, SK15

BAK4, BK7, and SK15 are all different types of prism glasses. We have two different kinds of prisms: the Porro prisms and the Roof ones, and they’re manufactured out of one of these three glasses.

  • BAK4 is the premium choice. It’s the most expensive, and it transmits the largest amount of light, creating the sharpest image possible.
  • BK7 is its more humble sibling, as it’s a lot more affordable while still maintaining an excellent image through the perfectly adequate light transmission.
  • Lastly, the SK15 is a mix of both, as it has a higher refractive index than both.


The numbers above relate to the coating that the lenses have undergone to provide protection against the elements, such as heat and cold. The coating also protects against reflection and glare.

  • If you have the number I, it means that one layer of magnesium fluoride was applied to the glass boundaries.
  • If you have the number II, then you have 5-7 layers of coating on the objective lens and one layer of magnesium fluoride on the glass boundaries.
  • If you have the number III, it means that you have 5-7 layers of coating on every glass surface of the binoculars, except the single coated prisms.
  • Finally, if you have IV, then you have 5-7 layers of coating on every glass surface of the binoculars, with no exceptions.

Remember, these coatings provide an extraordinary level of protection, and therefore, they extend the lifespan of your binoculars.

2-4 mm

If you find a number in millimeters and ranges between two and four, this number definitely relates to the exit pupil size. The exit pupil is the diameter through which the light can leave the binoculars into your eyes.

According to how light or dark the room is, your own pupil size ranges between 1.5 mm and 8 mm. Hence, the exit pupil being somewhere between 2 and 4 mm, is quite adequate.

8-18 mm

You can find another number in millimeters; however, this one falls between 8 and 18. This one relates to eye relief.

Eye relief is simply the difference between keeping the binoculars laid on your eyes till they imprint on your face so that you can see clearly, and having them placed comfortably at a reasonable distance from your eyes while still maintaining a full wide view.

The presence of eye relief is essential for your comfort and enjoyment of your trip. Plus, it’s incredibly useful for people who wear glasses, as it allows them to wear their glasses without having the binoculars press onto them, which can cause headaches.

Final Thoughts

We hope that we’ve provided you with all the proper simplified answers to the dilemma of “what do the numbers on binoculars mean?”

You need to know that each number is significant on its own; however, combining them will give you the final product. Some of them are proportionally related, while others are inversely related.

Furthermore, the highest of each isn’t always the most suitable choice for you. Always know your usage plan for binoculars, as that’ll be the determining factor in the specs you’ll need and how much money you’ll have to spend to obtain these features.

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