What Do Scope Numbers Mean? – A Brief And Simple Guide

Most firearm enthusiasts own more than one type of firearm, and when you start to look at ‘ranged weapons’ like a rifle, pellet gun or sniper rifle, accuracy beyond the naked eye becomes paramount.

So most people start looking for scopes, but if you are new to them there’s a bewildering array of numbers, so what do these scope numbers mean?

A rifle scope is defined by its lower magnification, its upper magnification limit, and its objective lens diameter. A typical scope might be referred to as 3-9×40. This means three times magnification as a minimum, the scope will be adjustable to 9x magnification and has a 40mm objective lens diameter. The larger the objective lens the more light enters the scope.

Additionally, on the specifications for a scope, you will see numbers for eye relief, MOA, parallax, length, weight, tube chassis, and field of view.

A scope without a magnification range, but fixed will be described as 4×40, or something similar. A single number preceding the x just means you will have no ability to alter the magnification.

a diagram of a rifle scope with explained parts

Unsurprisingly, using iron sights on a ranged weapon can be risky. The naked eye is only capable of producing so much accuracy.

A good scope means much tighter groups at the longer ranges, which means the difference between an accurate hit and a miss.

Try using iron sights on an AR-15 at 100 yards and see what your grouping is.

Even the budget scopes come with magnification, so a shooter can now easily zoom in to a distant target and get fantastic accuracy. What could be wrong with more shots on target?

The scope is part of your rifle and people tend to forget it’s actually part of each shot. A good scope selected for your needs can make or break an accurate shot.

rifle scope sight picture to paper target

Scope Description And Specifications – What Are We Talking About?

So, taking our example again, let’s say you see a scope described as 3-9×40.

Let’s discuss further what each number actually means.

3 – Singularly this might be referred to as 3X which means three power. That is that as a minimum for this particular scope (ie when zoomed out) the target object will look three times closer than it does with the naked eye.

9 – So this figure means 9X or nine power. This represents the maximum zoom of the scope and so the target object will appear nine times nearer than it does with a naked eye.

The 3 and the 9 come with a dash between them (3-9×40) which thus indicates the magnification range of scope. A scope described thus will feature a power ring near the ocular lens that will zoom in and out.

x40 – The objective lens has a 40mm diameter. This diameter gives you an idea of how much light the scope will let in, so it could be better for night shooting the larger it is. It also indicates how clear and bright the sight picture may be. However, a larger diameter means a heavier scope, they are generally more expensive and there is more chance of lens glare for the hunters.

Taken all together the whole scope would be called a ‘three to nine by forty’.

Exactly how much objective lens is needed by a shooter will largely depend on the usage of the rifle. A 5-25×50 scope will be oversized for a pellet gun but OK for a longer range sniper rifle.

So it’s usually a good idea to fit the objective lens to the distance you are shooting at.

  • Approximately 100 yards a 28mm to 32mm diameter objective lens
  • Approximately 100 yards a 32mm to 44mm diameter objective lens
  • Approximately 250 yards a 50mm or so objective lens might a good bet

a selection of scopes of several rifles

What Are The Other Specification Numbers For A Scope

When looking at a scope, the magnification and objective lens diameter is normally part of the manufacturers titling of their equipment

As in say the Hawke Vantage 3-9×40 or the Vortex Optics Diamondback 6-24×50.

That’s the format it normally comes in, the company name, the model, minimum magnification, maximum magnification and finally the objective lens diameter.

However, these are not the only numbers associated with the scope.

Let’s run through them.

Field of view – Quoted in feet or degrees at a specific distance (eg 8.7-2.9m @100m)

This is the size of the view area that is witnessed as you are looking down the rifle scope. It is directly connected to the magnification, because as you zoom in the visible area gets smaller. A large field of view is more necessary for moving targets

In the above example, with 8.7-2.9m @100m this means that on maximum zoom a target that was 2.9m wide would fill the scope sight picture. At minimum zoom it would have to be 8.7m to do the same.

A scope used for spotting will have a wider field of view than a sniper scope, as will scopes that might require fast target acquisition.

rifle scope sight picture to wooded area

Eye relief – Quoted as a distance, such as ‘eye relief: 89mm’

If your eye was right next to the rear lens of the scope (ocular lens) then eye relief is the distance you need to back away so that the full field of view is visible. On very powerful round cartridges and calibers your eye does not want to be too near the scope eyepiece when the cartridge detonates. Recoil, people..

MOA – Quoted as an angle or degrees, or a fraction of MOA (eg ¼ MOA)

MOA stands for ‘Minutes Of Angle’. It’s a unit of measurement for a circle, and is 1.0472 inches at 100 yards which is so close 1 inch that that is how it’s expressed. A scope reticle might be 2MOA for example.

So it’s 1 inch at 100 yards, 2 inches at 200 yards, and 3 inches at 300 yards and so on. It measures the distance that the angle differs by as you extend the length of the shot.

Exit Pupil – Quoted as a length, usually in mm (eg. Exit pupil: 13-4mm)

As light enters the objective lens of the scope it travels down the tube and exits the ocular lens where you get a sight picture. The exit pupil is a circle of light exiting the scope that enters the eye. 

A very small exit pupil isn’t good enough to make the image bright and clear. The larger the exit pupil the better it will be in low light conditions.

The human iris is approx. 2-3 mm during daylight, 4-5mm in darker conditions like dusk, and 6mm as darkness envelops.

Focus/Parallax – Quoted as a range of distances, usually meters to infinity (eg. Focus/Parallax – AO 9m – ∞, or 9m / 10yds to Infinity)

Parallax describes the movement of the reticle while on target as you move and bob your head slightly. It’s not a good thing in terms of accuracy, and parallax free would mean that as you moved your head, the reticle would stay positioned on the target.

So you want as little parallax as possible.

If you could put your eye ‘dead center’ each time, that’ be great but as humans, we have slight nuances. Good shooters have a ‘feel’ to their aiming position.

If you can move your eye a little off dead center and the crosshair, dot or reticle remains absolutely on target then you have a ‘parallax free’ firing situation with the scope.

Parallax is often confused with focus, but they’re not the same. When parallax is adjusted it cancels out the parallax between the reticle and the target at a given range,

Thus the two numbers quoted are the range where you can cancel parallax. In a ‘9m / 10yds to Infinity’ parallax scope, anything below 9m aiming you will get parallax.

Tube diameter – Quoted as a length, usually 1 inch (eg. Mono-Tube Chassis: 1 inch)

Most scopes will have a central tube of a 1 inch diameter. Sometimes it’s quoted in mm, say 30mm or 34mm. A larger diameter of tube will be slightly more rigid, and likely to be more durable.

The larger tube diameter allows for more elevation adjustment, which is useful if you are a long range shooter. As scopes attach to a mount, this figure means you will have to buy scope rings of a size suitable for the scope tube.

a young girl with a bolt action rifle

Length – Quoted as a length, either in mm or inches (eg. Length: 349mm)

This isn’t internal distances, but the obvious, the actual length of the scope.

Weight – Quoted as a weight, either in ounces, grams or kg (eg. Weight: 600g)

Again, this isn’t anything other than the obvious, the actual weight of the scope, without mounts, rings, or packaging.

Increments – Expressed as a fraction of the MOA (eg. Elevation Increment 1⁄4 MOA)

Every scope has a windage and elevation increment turret. This figure refers to the amount of movement of one click of the turret. 

So if you adjust a ¼ increment scope upwards by 1 click then the scope will put the reticle ¼ MOA above where you are shooting.

It’s done as an angle to negate the differences at different distances. 4 clicks upwards would mean 1MOA which is 1 inch at 100 yards and 2 inches at 200 yards.

So if you want to adjust the scope when firing at 100 yards up and inch it’d be 4 clicks up. If you want to adjust the scope up an inch at 200 yards, it’d be 2 clicks.

What Does 4-16×50 Mean On A Scope

Scopes are built for a wide variety of situations, even though their principle aim (pun intended) is to help achieve better accuracy.

So with our example of 4-16×50, let’s run through it.

4 – This is the minimum magnification you will get as a sight picture. Fully zoomed out you will see the target 4 times nearer than with the naked eye.

16 – This is the maximum zoom your scope will allow. Fully zoomed in the sight picture will be 16x closer than with the naked eye.

This sight will have a magnification ring, also called the power ring to zoom in and out between 4x and 16x magnifications.

50 – This is the objective lens diameter, so it will be a large scope. The scope will let in more light than a 32mm lens, so be better at shooting in low light conditions.

This likely to be a large scope and capable of shooting in lower light with a bright sight picture.

It’s generally agreed that 10x is the minimum for 1000 yards, so this scope will be capable of seeing those kinds of ranges.

What Does 4-12×50 Mean On A Scope

So let’s go with another example of 4-12×50, and run through it.

4 – This is the minimum magnification you will get as a sight picture. Fully zoomed out you will see the target 4 times nearer than with the naked eye.

12 – This is the maximum zoom your scope will allow. Fully zoomed in the sight picture will be 12x closer than with the naked eye.

This sight will have a magnification ring, also called the power ring to zoom in and out between 4x and 12x magnifications.

50 – This is the objective lens diameter, so it will be a large scope. The scope will let in more light than a 32mm lens, so be better at shooting in low light conditions.

Again, this is likely to be a heavy scope capable of shooting in lower light with a brighter sight picture.

Taking the fact that 10x is the minimum for 1000 yards, at only 12 times magnification you are maxing out the scope at this range.

This scope would be more suited for the 500 to 1000 yard shooting range.

a rifle and scope on a pelt

What Does 6-24×50 Mean On A Scope

So let’s go with another example of 6-24×50, and run through it.

6 – This is the minimum magnification you will get as a sight picture. Fully zoomed out you will see the target 6 times nearer than with the naked eye.

24 – This is the maximum zoom your scope will allow. Fully zoomed in the sight picture will be 24x closer than with the naked eye.

This sight will have a magnification ring, also called the power ring to zoom in and out between 6x and 24x magnifications.

50 – This is the objective lens diameter, so it will be a large scope. The scope will let in more light than a 32mm lens, so be better at shooting in low light conditions.

Again, this is likely to be a heavy scope capable of shooting in lower light with a brighter sight picture.

This scope is for more serious accuracy at long range. The increased magnification power means the reticle will be smaller on target. Specifically a 1000 yards plus scope.

What Does 2-7×32 Scope Mean

So let’s go with another example of 2-7×32, and run through it.

2 – This is the minimum magnification you will get as a sight picture. Fully zoomed out you will see the target 2 times nearer than with the naked eye.

7 – This is the maximum zoom your scope will allow. Fully zoomed in the sight picture will be 7x closer than with the naked eye.

This sight will have a magnification ring, also called the power ring to zoom in and out between 2x and 7x magnifications.

32 – This is the objective lens diameter, so it will be a large scope. The scope will let in more light than a 28mm lens, but not as much as the 50mm.

With only 7 times magnification power this is a scope for shorter ranges, and might be more suited to an airgun than a rifle if accuracy is needed. Additionally, as dusk beckons the sight picture will get darker.

a close up of a scope, side view

What Does It Mean When A Scope Is 4×32

Throwing in this one to confuse you, as now we are missing a power range.

So what does a scope with the specification of 4×32 mean?

It simply means the magnification is fixed. Most scopes have a power range adjustable by the power ring to zoom in and out. A scope marked 4×32 wont.

It’s not a small scope but is pretty much only useful if you are shooting at specific ranges, and the range of your shot doesn’t change much. Probably up to 100 yards in this case..

Scope Magnification For 500 Yards

As always with scopes, many people select their shooting usage first and then decide what scope they will need.

So if you are shooting at 500 yards, what scope is appropriate. The 10x rule as a minimum for 1000 yards is only the limit, but a good 4-16×50 should easily do the trick.

Scope Magnification For 1000 Yards

The minimum for this range is considered 10x power magnification, but the reticle might cover a good 10 inches of the target.

Going for a scope designed for this range like a 6-24×50 gives you the magnification power to really zoom in, and get the accuracy.

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