One essential component to pay attention to when buying a rifle scope is the numbers associated with it. They can tell you everything from whether it’s fixed magnification or variable, as well as how large the scope is.
If you disregard these numbers, chances are you’ll end up with a scope not fit for your purposes. So, let’s take a closer look at them and what else to look out for.
And for more on scopes see our guide to the best DMR scope out there.
What Do the Numbers on a Scope Mean?
The numbers on a rifle scope are separated by an X. On the left side of the X, you have the scope magnification. On the right side is the size of the objective lens. For example, for a fixed magnification rifle scope, the numbers may be 3.5×50.
Here’s a breakdown of these terms and how they can affect the quality and reliability of your scope.
There are two primary types of rifle scopes – a variable scope and a fixed scope. A variable magnification scope will have two numbers, such as 1-12. This means the scope can magnify your image from 1x to 12x.
As a general rule, every 1x of magnification power makes an object at 100 feet look like it’s one foot away. So, the higher the magnification range, the easier it is to spot targets that are further away. (Reference: Rifle Scope Numbers)
By comparison, a fixed rifle scope can’t be adjusted. So, if the scope reads 3.5x, you’ll always see objects at that magnification power, no more and no less.
Objective Lens Diameter
The objective lens of a rifle scope is the glass piece that’s furthest away from your eye. So, the piece you look through is the eyepiece, and the other side is the objective lens.
The objective lens diameter matters because it determines both the size of the rifle scope and how much light can enter. As a rule, the more light that enters the scope, the easier it is to see your target.
Typically, a variable rifle scope will have a larger objective lens, especially if it can magnify at great distances (i.e., 25x or more). The objective lens diameter is also represented by mm, so a 5×50 scope would have a 50mm lens.
Picking the Right Scope Size
No matter what firearm type you’re using, you need to make sure you have the right size scope for your needs. So, you must pay attention to whether it’s fixed or variable and the size of the objective lens.
While it may be tempting to go with a larger scope with a higher variable magnification range, that doesn’t make sense if you’ll be shooting targets up close. There is such a thing as too much magnification. Instead, it’s best to get the best size for the type of shooting you’ll do the most.
For close-range shooting (i.e., 100 yards or less), you may want a fixed rifle scope. This way, you don’t have to adjust the zoom settings each time you take aim. For mid-range shooting (i.e., 100 to 500 yards), a variable scope is likely better.
As far as the objective lens, you don’t need a massive scope if you’re not shooting long-range. As a rule, a 30-40mm lens works well for close and mid-range targets, while a 50mm version is better for longer distances.
Is a Bigger Objective Lens Better?
The objective lens size determines how much light will enter the scope. While a larger lens often means better clarity, it’s not always necessary. If most of your shooting takes place within the 500-yard range, you don’t need a massive rifle scope.
Another point to consider is how you’ll use your scope in action. For example, if you’re doing a lot of close-quarters shooting, a bigger lens may be cumbersome and harder to manage.
Snipers generally need the largest objective lens diameter, while those engaging in CQB can get away with a much smaller model.
What is the Objective Lens on a Rifle Scope?
The objective lens is the front glass piece of the scope. The size of this lens determines how much light can enter, affecting how well you can see your target. Typically, on a fixed scope, the lens is smaller than it is on a variable scope.
Where to Find the Numbers on a Rifle Scope
Most rifle scopes will have the magnification setting and objective lens diameter listed in their name. For example, the Vortex Viper PST 1-4×24 Riflescope tells you that it’s a variable scope with 1-4x zoom and a 24mm objective lens.
Also, many rifle scope numbers will be printed on the side of the scope itself for easy reference.
Other Scope Numbers & Features to Consider
While the primary numbers on a rifle scope represent the magnification and objective lens, those are not the only numbers that matter. Here’s a rundown of other features that have numbers associated with them.
Eye relief is the distance your eye needs to be from the end of the scope to see through it clearly. With most rifles, you can get away with 3.5 inches. However, guns with a heavier recoil (i.e., sniper rifles or large caliber guns) need a bigger eye relief.
You can find the eye relief number when looking at the specs for a rifle scope. Typically, those with a shorter zoom range also have shorter eye relief.
You won’t find the exit pupil numbers listed on a rifle scope’s spec sheet. Instead, you’ll have to calculate this yourself.
The exit pupil is the amount of light coming out of the scope and into your eye. The higher the number, the easier it is to see in low-light conditions.
To calculate the exit pupil, you’ll need to divide the size of the objective lens by the maximum magnification setting. For example, with a 1-8×40 scope, the exit pupil will be 5mm (40/8).
For reference, the maximum amount of light the human eye can experience is 7mm, so the closer you get, the easier it is to see at dusk or at night.
Field of View (FOV)
The field of view refers to the amount of scenery you can see inside the rifle scope as you look through it. Unfortunately, it’s hard to determine an exact field of view as it changes from one scope to the next. There may also be differences between manufacturers, even if the size and magnification of the scopes are identical.
So, as far as scope numbers, you may not be able to calculate a precise field of view. However, if something is listed, it refers to what you can see at 100 feet. So, a wide field of view allows you to spot your target more easily.
Also, as you zoom in with your scope, the field of view gets narrower. So, at 15x zoom, you’ll only see a fraction of what’s available at 1x zoom.
Elevation and Windage Adjustments
Looking through a scope involves a lot more than just identifying your target. The knobs on a scope also allow you to compensate for windage and elevation. Without these adjustments, it would be impossible to be accurate at longer distances.
Elevation and windage numbers are represented by either MRAD or MOA settings. MRAD stands for milliradians, and MOA means minute of adjustment. Most shooters prefer MRAD because it’s the gold standard, but MOA adjustments are also easy to master.
When using windage and elevation adjustments, it helps to create a DOPE sheet. DOPE stands for Data on Previous Engagements, and it allows you to make adjustments quickly and accurately.
Parallax occurs when your lens isn’t focused properly, causing the reticle to move around while aiming. Most rifle scope manufacturers will compensate for parallax at a certain distance, such as 100 yards. In other cases, you may be able to adjust the parallax on the fly.
The reticle is the part of the scope you use to pinpoint your target. The classic version of a reticle is a set of crosshairs, where the intersection is where you aim your bullet.
There are quite a few types of reticles, each offering its benefits and downsides. Here are some common ones:
- Bullet Drop Compensation (BDC) – This reticle shows you how much your bullet will drop at various distances. This way, you can compensate accordingly.
- Red Dot – As the name suggests, this reticle is just a red dot in the center of the glass.
- German Reticle – This option has lines on three sides but not the top. Also, the bottom center line has an arrow-shaped tip for accuracy.
- Mil-Dot – This reticle has lines on each crosshair so you can match your windage and elevation adjustments.
- Duplex – Rather than using solid crosshair lines, a duplex reticle will be thicker on the outside and thinner toward the center.
Since you need to see your target at various distances, you need a rifle scope with high-quality glass. As a rule, the better the glass, the more light comes into the scope, offering better clarity.
Also, premium scope glass comes at a price, so you must be prepared to spend extra to get the best option. Typically, brands like Vortex and Leupold have the best glass, but other brands can also have pretty amazing results.
The aperture is another term for the size of the objective lens. So, if you have a rifle with a 50mm lens, you could also say it has a 50mm aperture. The larger the lens, the more light comes in, offering better visibility, particularly in low-light conditions.
Numbers on a Rifle Scope Example Chart
|Scope||Variable or Fixed?||Magnification||Lens Size||Eye Relief|
|Vortex Viper PST||Variable||1-4x||24mm||4 in|
|Leupold FX-II||Fixed||4x||28mm||18 in|
|Steiner P4Xi||Variable||4-16x||56mm||0.5-4 in|
|Primary Arms Classic||Fixed||6x||32mm||3.1 in|
|Vortex Crossfire II||Variable||2-7x||32mm||9.45 in|
Examples With Different Scope Models
As you can see from the chart above, most scopes stick within a certain range. However, one outlier is the Leupold FX-II.
The reason this scope has such a large eye relief is that it’s made for handguns, not rifles. I’ve included it to illustrate the variations you can find based on how the scope is meant to be used.
Otherwise, most scopes will stick within the 1-8x magnification range. As far as the aperture, they’re usually within 24-40mm. If you’re shooting at longer distances, you’ll want something like the Steiner with a 56mm lens.
Overall, the type of scope you choose depends on what you plan to shoot. If you’re after big game, you want something that’s accurate at 300 yards or so. However, if you’re sniping, you want a scope with a higher magnification range and a larger lens.
For more reading see our write up on what is a 4×32 scope and what does 4-16×50 on a scope mean.
- Magnifying Patrol Rifle Scopes Assessment Report, Department of Homeland Security. Retrieved from: https://www.dhs.gov/sites/default/files/publications/Mag-Patrol-Scopes-AR_0114-508_0.pdf
I have been writing firearms and outdoor material for over 50 years to date. I have hunted across the world, including Russia, and a great deal of time professional hunting in Australia. I currently live in the American West and hunt all across the Black Hills of South Dakota and the Big Horn Mountains. I have specialized much of my work as a load developer in shotguns and rifles. I have run a small company that builds suppressor barrels of my design and load tests for writing purposes and consulting. My commercial names include Ballistics Research & Development / Metro Gun Systems TM.
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