What Do The Numbers Mean on a Rifle Scope?

Rifle owners looking to add distance and accuracy to their shooting game need to invest in a scope. The good news is that rifle scope manufacturers are not short on the ground. Their scopes are offered in various configurations and at prices to suit everyone’s pocket.

But, which one is for you? This will depend upon such things as your shooting application, expected target distances, and budget. However, one thing they all come with is a series of numbers. So, before making any rifle scope decision, a very important question needs answering: What do the numbers mean on a rifle scope?

Before getting into scope numbers and what they mean, let’s look at:

what do the numbers mean on a rifle scope

How a Rifle Scope Can Change Your Shooting Game?

When it comes to spotting and acquiring distant targets, a rifle scope is invaluable. This is because the naked eye can only clearly identify things within your normal range of vision. Using a rifle scope helps you to locate and then focus in on distant targets. Once a target is acquired, you can then place shots with accuracy.

It is magnification that dictates the distance a scope is capable of. This is based on a principle that scope manufacturers across the globe follow, in that the starting point of magnification is always measured against a person with 20/20 vision. This is classed as normal vision acuity (the clarity or sharpness of vision).

So, whatever power a scope is adjusted to, it will magnify that number of times against what the naked eye sees.

How does scope magnification work?

Adjust a scope to 3x power, and your target will magnify to 3 times larger than the naked eye can see. Adjust it to 20x power, and the target will magnify to 20 times larger than what the naked eye would see.

Therefore, if you view a target through a scope on 3x magnification, it will appear to be three times closer than its actual distance. For example, targets at 300 yards will appear to be 100 yards away.

As you increase magnification, the apparent distance to your viewed target image will decrease in direct proportion. For example, double the 3x magnification mentioned to 6x. This will cause the target image to appear half as far away.

what do the numbers mean on your rifle scope

But, there is an additional benefit…

When doubling magnification (as per the 3x to 6x example), this also results in doubling the apparent target size.

As can be seen, rifle scope magnification gives a two-fold benefit. It brings your target closer and increases its size.

While on the topic of magnification, let’s take a quick look at the two main scope types that are of particular interest to rifle owners…

Fixed and Variable Magnification

Scopes come in many flavors! However, two general categories for rifle scopes are Fixed magnification and Variable magnification. As will be seen, one style is now far more popular than the other.

Fixed Power (Fixed Magnification)

As the term suggests, choosing a fixed power scope will give you magnification but only at one power setting. Examples being 4x, 6x, 8x, and 10x magnification.

Fixed power scopes have been around a long time; in fact, manufacturing started way back in around 1850 in the U.S.! Various conflicts throughout the world saw improvements in rifles and scopes developed as well. They were also the first type of scope to really attract civilian rifle shooters en-masse.

The models offered were acceptably priced, relatively easy to use, effective, and highly popular. Ask any shooting buddy who was active in the ’60s, ’70s, and ’80s, and most will have a fond story (or three!) to tell of their first fixed power rifle scope.

You see what you see…

They are a basic type of rifle scope and come with no zoom in/out. The view you see is what you get. On the plus side, fixed power scopes are brighter at their given magnification level than a variable power scope on the same setting. You will also find that because there are fewer moving parts, there is less to go wrong with them.

Although not set in stone, fixed magnification scopes also tend to be less expensive than variable power scopes.

On the decline…

Since the 1990s, there has been a gradual decline in companies that manufacture fixed power scopes. This is because many now concentrate on producing scopes with variable magnification.

However, some quality companies such as Leupold, Hawke Advantage, and Burris still produce fixed magnification models. It is also clear that this type of scope is not dead in the water. Anyone looking to take fixed magnification a step further needs only to look at Trijicon’s ACOG scope range. These models really are a force to be reckoned with, although they do buck the ‘cheaper’ price tag comment just mentioned!

Variable Power (Variable Magnification)

Rifle scopes with variable magnification are now all the rage. They can be adjusted from one power setting to another with ease. This is through a rotating power adjustment ring positioned on the eye piece. With clearly marked numbers indicating magnification levels, this means rapid change in magnification is yours.

Top-end magnification on variable power scopes now comes with an extreme of 50x or 60x. However, this is rare, and most shooters settle for far lower power. A good example is the fact that 3x to 9x variable magnification is a highly popular choice with hunters.

what do numbers mean on rifle scope

What Do The Numbers Mean on a Rifle Scope?

When looking at rifle scopes, you will come across various numbers that need understanding. The most prominent will be the Magnification offered and Objective lens size.

Before explaining this set of numbers, here’s a quick explanation of a scope’s two main lenses…

When looking through a scope, the ocular lens is the one closest to your eye. The front lens, which is the farthest from your eye, is called the objective lens. It is the size of the objective lens (in millimeters = mm.) that is prominently displayed with the magnification offered.

Breaking these numbers down makes them easy to understand…

Fixed Magnification Scopes

When looking at scopes with a fixed magnification, you will see two numbers – Here are a few examples:

6×42 – The first number (6) indicates the fixed magnification power. The second number (42) is the objective lens size in mm.

4×32 – The first number (4) indicates the fixed magnification power. The second number (32) is the objective lens size in mm.

Variable Magnification Scopes

Variable magnification scopes have three numbers as opposed to the two numbers for a fixed power scope. The first two numbers indicate what range (minimum to maximum) of variable magnification the scope gives. The third number is the objective lens size in millimeters.

Here are two examples:

3-9×40 – This means you will get between 3x and 9x variable magnification and a 40 mm. objective lens.

5-20×56 – This means you will get between 5x and 20x variable magnification along with a 56 mm. objective lens.

The Exit Pupil and Magnification

The next number to look at is the exit pupil. Similar to the objective lens size, this is usually stated in millimeters. But before looking at exit pupil sizes, let’s define exactly what it is.

The exit pupil is the light-based circular image the scope presents to your eye. It determines such things as how much light is passed through the scope to your eye, how clearly you can see objects, and how bright a target image is under low-light conditions.

In general, the larger the exit pupil, the brighter your view. This is because more of your viewing eye will be bathed in light. A large exit pupil can also give an advantage in limited target view situations. Finding some kind of eye position when faced with a “once or never” shot is crucial. A larger exit pupil can offer that.

But, it is not all win-win with a larger exit pupil…

It really is “horses for courses.” Those who prefer daytime shooting with bright sunshine will be better served using a small exit pupil. This is because, during daylight hours, the pupils of your eye are only around two millimeters in diameter. This means that too much light through your exit pupil could hinder your view.

For those who prefer shooting in low-light or darkness, the opposite is true. During such conditions, your pupils dilate to between 5-8 millimeters. This means a larger exit pupil will serve you well.

Scope specification sheets should always give exit pupil sizes, but there is a straightforward equation to work them out, which is to divide the effective objective lens diameter (in mm) by the magnification.

Here’s a fixed magnification scope example:

4x-32 – This is a 4x fixed magnification scope with a 32 mm objective lens. Divide 32 (Objective Lens diameter) by 4 (Fixed Magnification) = a generous 8 mm exit pupil.

what do the numbers mean on the rifle scope

Variable magnification scope example:

Because there are different magnification levels (Minimum to Maximum), the exit pupil size is also variable. It changes depending on what magnification setting you have it on. For example, a 3-9×40 rifle scope comes with variable magnification between 3x and 9x and has a 40 mm objective lens.

Divide 40 (Objective Lens diameter) by 3 (Minimum magnification setting) = a 13.1 mm. exit pupil.

The size of the exit pupil will reduce as each magnification step is increased. Taking the above example and having your scope on maximum 9x power setting, you would:

Divide 40 (same objective lens size) by 9 (Maximum magnification setting) = 4.4 mm. exit pupil.

Just to square this one away. If you put this 3-9×40 scope on 5x magnification, the equation would be:

Divide 40 (same objective lens setting) by 5 (5x power setting) = 8 mm – Nice size for nighttime shooting!

So, a 3-9x-40 rifle scope has an exit pupil that varies between 13.1 and 4.4 mm. (Minimum to Maximum magnification settings).

Field of View (FOV) and Eye relief

Two more interesting numbers relate to eye relief and FOV. Eye relief on a rifle scope is seen as being the ideal distance between the human eye and the scope’s eyepiece. Having this allows shooters to obtain the full viewing angle. Most scopes will come with eye relief measured in inches. In general, a low magnification scope will have larger eye relief than a scope with high magnification.

Please do not treat eye relief as an afterthought…

The heavier your rifle’s recoil, the greater your chance of suffering eye or facial injury every time you fire. Err on the side of caution and look at nothing less than 3.5 to 4-inches+ of eye relief.

Field of View (FOV)

A human’s field of vision comes in at around 210 degrees in a horizontal arc. Scope FOV is classed as the area size you see when looking through a rifle scope. Numbers generally relate to how many feet you can see at 100 yards. (Note: FOV can also be measured in degrees against the same 100 yards).

A scope’s FOV is directly related to magnification. This means that as you magnify a target, the closer your FOV will get. Scopes with higher magnification will have a smaller field of view. If your aim is to achieve rapid target acquisition or to follow moving targets, a larger FOV is the way to go.

Design processes will define how a manufacturer measures a scope’s FOV. Although, this should not vary too greatly. To give you an indication of what to expect, let’s use the 3-9×40 variable magnification scope as an example.

When on its lowest 3x magnification setting, it will give around 33 feet at 100 yards. When turned up to its 9x highest magnification, your FOV would be around 12 feet at 100 yards.

One other example shows the approximate FOV expected from a higher magnification scope. Take a quality 6.5-20×50 variable magnification scope. At 6.5 lowest magnification, you would get a FOV of around 19.5 feet at 100 yards. Whizz it up to its highest 20x magnification, and the FOV you could expect at 100 yards would be around 6.3 feet.

Using a Rifle Scope Can Give You Multiple Benefits!

Let’s finish with a number. But this time, the choice is yours, and the figure chosen will relate to the multiple benefits a well-chosen rifle scope offers. I will get you started with an absolute minimum of 3x!

First, it will allow you to gradually increase your accuracy over different distances. Second, this improvement will keep pace with your continuing sense of achievement. Then add these together, and your third benefit will come from an increasing level of shooting enjoyment!

Just remember, the use of a rifle scope will bring variable rewards, and they are yours to find.

Looking for a Quality Scope?

Then check out my in-depth reviews of the Best Scopes for M&P 15-22, the Best Low Light Rifle Scope, Best Rimfire Scopes, the Best Air Rifle Scopes, as well as the Best Deer Hunting Scopes you can buy in 2022.

Or, take a look at our in-depth reviews of the Best 308 Rifles Scopes, the Best 300 Win Mag Scopes, the Best Mini 14 Ranch Rifles, the Best Mil Dot Scopes, the Best Scout Scopes, or the Best Scopes for AR15 under 100 Dollars currently on the market.

Final Thoughts

A full understanding of the different numbers on a rifle scope is something you owe yourself. Rifle scopes cost hard-earned money. Armed with such knowledge, you will be in a position to make an informed purchase decision.

The scope numbers that I’ve covered are key rifle scope measurements. Hopefully, the explanations and examples given have left you with a better understanding of what these figures stand for.

Use this information to decide the type of scope and a realistic maximum magnification. Don’t over-egg maximum power levels; this is a mistake many make. Then consider your shooting application and how regularly you can get out on shooting sessions. By looking at these factors and sticking to a firm upper budget limit, one thing is for sure:

There is a scope out there with your name on it!

Happy and safe shooting.

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About Gary McCloud

Gary is a U.S. ARMY OIF veteran who served in Iraq from 2007 to 2008. He followed in the honored family tradition with his father serving in the U.S. Navy during Vietnam, his brother serving in Afghanistan, and his Grandfather was in the U.S. Army during World War II.

Due to his service, Gary received a VA disability rating of 80%. But he still enjoys writing which allows him a creative outlet where he can express his passion for firearms.

He is currently single, but is "on the lookout!' So watch out all you eligible females; he may have his eye on you...

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