Gauge vs. Caliber: How to Measure Up Your Shotgun’s Performance

If you possess a shotgun, the first thing that you should understand is the difference between a caliber and gauge. My collection of shotguns is quite diverse, but one thing that enhances my performance and enables me to select the best model from my collection is the accurate understanding between these measurements.

So if you are looking to revolutionize how you tackle your shotgun and become a pro at the game, this article will definitely help you.

Caliber and gauge are two different systems of measurements that have some similarities among them. They both refer to the diameter of a projectile that is fired from a shotgun. Quite simply, a gauge represents the exact number of items of a particular diameter that is equivalent to a fixed weight. On the other hand, a caliber is the nominal diameter of a bullet in millimeters or inches.

The term bore is more commonly associated with gauge, whereas the term inner barrel dimension is used in relation to the caliber. But that’s not all; you will have to read ahead to know more about these terms.

What Does Gauge Mean?

In the simplest term, a gauge is an instrument used to give a visual display of the level, amount, or contents of something. It also acts as a numerical representation of the diameter, such that the larger the number on the gauge, the smaller is the diameter of something.

For instance, a 12 gauge will be bigger than a 20-gauge shotgun. Similarly, a 10-gauge wire is wider than an electrical gauge wire of 16. In both of these instances, the smaller the item, the bigger will be its gauge number. This may seem counterintuitive to some people, but there are perfectly adequate reasons for why this is so.

gauge vs caliber

When it comes to shotguns, the gauge will be the number of lead balls of a particular diameter equivalent to a pound. If you made lead balls the diameter of a 12 gauge shotgun bore, it would require 12 of these to equal one pound. On the other hand, if you take 20 lead balls, it would fit the diameter of a 12-gauge shotgun.

In this way, the larger balls come with a smaller number because it takes fewer of these shells and balls to equal a pound. This makes sense, right?

However, now you may wonder what happens if you have a 410 gauge shotgun? Would the same principles apply? Well, not really. There is no such thing as a 410 gauge shotgun. Instead, there is a 410 caliber shotgun, but more on that later.

History of the Term

Gauges are one of the oldest measures of thickness that originated in the British iron industry. This was at a time when there was no other universal unit of thickness. To address the concern, gauges were used to measure and describe thickness of objects in fractions of an inch. The inventor, Eugene Bourdon, was a brilliant watchmaker and engineer who is revered among French people for this amazing invention in 1849.

When it comes to lead balls, their particular size (and shape) were used to be achieved in so-called shot towers, where the molten lead was poured through a sieve with hole sizes corresponding to the gauge required.

How Gauge is Measured?

AWG, also known as the American Wire Gauge, represents the wire gauge sizes through numerical values. The lower the number of a wire, the larger its diameter will be.

The exact calculation is a complex process that is usually carried out by experts. When you purchase a shotgun, the seller will tell you the gauge measurement. It is also interesting to note that the most common size is 12 gauge, and nearly 50% of all shotgun markets in the USA sell this kind. However, shooters who are uncomfortable using a 12-gauge gun mostly choose to go with the 20-gauge shotgun.

Before purchasing your model, make sure you check the number labelled on it. This will accurately tell you the gauge measurement of your gun.

shotgun caliber

What does Caliber Mean?

When it comes to shotguns, caliber is a widely used term. It is a measure that indicates the interior diameter of a shotgun barrel. Moreover, it measures the diameter of a shotgun’s ammunition. It is mainly measured in inches or millimeters, but there is more to the story.

For your clarity, let’s see a couple of examples. For instance, a 9mm luger bullet and its inner barrel are around 9 mm in diameter. The number is rounded off to a whole value due to marketing purposes, and the exact diameter may be slightly higher or lower; however, that doesn’t hold much relevance here. The important thing is that the bullets and the barrel measurements are approximately the same.

If you are still confused, let’s look at another example. The 7.62 NATO/.308 win bullets are also 0.398 inches in diameter. The caliber measurement therefore allows the bullets to perfectly fit into the shotguns.

Now, I mentioned earlier that 410-gauge shotguns don’t exist. Here is why: 410 caliber shotguns can shoot a shell that is about 0.410 inches in diameter, which is precisely why it’s measured in caliber and not in gauge.

Another thing to remember is that caliber can be measured in both metric and Imperial measurements. This is to ensure that shotgun owners in different parts of the world can better understand their guns. So a 310 caliber shotgun can also be called a 7.94 mm caliber gun. Consequently, the bullet diameter can be 0.312 inches or 7.94 mm.

shotgun gauge vs caliber

How Caliber is Measured?

Caliber is a measurement of the diameter of the inner barrel and is expressed in hundredths of an inch, thousandths of an inch, or mm. It is important to note that there is no standard established to represent the value of the caliber. In most cases, the caliber is the bullet’s diameter and the distance between the grooves of the shotgun.


Growing up as an officer’s kid, I was surrounded by all kinds of shotguns at home. This made me understand the specs, features, and accessories of shotguns like very few others my age.

One thing that confuses many people using or considering to use a shotgun is the difference between gauge vs caliber. These are both systems of measurements and hold a great many similarities among them, making the confusion perfectly legitimate.

However, I hope that I managed to clear it out for you. One last thing remains for you: choose a shotgun with the gauge and caliber properties which fits your style and the chosen clay shooting discipline.