Rifle Scope Main Tube Measurements and Sizes

What is the real difference between scopes with different tube sizes? Does one size offer an obvious benefit over the other, or is it a secret ploy to sell more scope rings because I always seem to have 30mm rings when I'm trying to mount a 1" scope. 

First, we knock out some of the easier questions like, what is the scope tube size and how is it measured? Simple, a 1” scope has a 1” diameter and a 30mm scope has a 30mm diameter main tube. I told you it was really simple.

At the moment there are three popular tube sizes used by scope manufacturers; 1”, 30mm and 34mm. While there is no golden rule for what tube size is used for a certain type of rifle scope they can be loosely categorized.

Rifle Scope Tube Sizes

1”: This tube size is mainly used in your average hunting rifle scope. The small tube size contributes to a very small form factor while also reducing the overall weight of the scope. The scopes usually have a smaller range of adjustment in windage and elevation which makes them a great choice for hunters or shooters that prioritize weight and size over adjustability. 

30mm: the 30mm tube size is mainly used in scopes aimed towards providing the shooter with a larger range of adjustment without sacrificing light transmission. They normally have a larger range of adjustment for windage and elevation with the obvious trade off of an increase in weight and size over their 1” counterparts. 

34mm: In recent years we have seen the introduction of the 34mm tube by many popular rifle scope manufacturers. You may have noticed a pattern by now but the main reason for the increase in tube size is… an increase in adjustability without having to sacrifice lens size in the main body of the rifle scope. These scopes are almost always geared towards long range precision shooters with their oversized elevation and windage turrets and multiple revolution capabilities. 

Those descriptions may seem a little vague and that is for good reason. There is no golden rule when it comes to categorizing tube sizes for rifle scopes. You can find 30mm rifle scopes with less elevation adjustment than some 1” scopes and you can probably find a 1” scope that is heavier than a 30mm scope. The best answer to the question, why does a certain scope have a certain tube size? It’s fairly simple, that’s the tube size that would fit all of the internal components. Rifle scope tube size is simply just packaging for the features and capabilities that a manufacturer decided to give a certain scope.  

In closing, tube size is not a direct reflection of the features or capabilities a rifle scope will have but rather it is an outcome of the construction of the internals of each individual scope. My advice to you is to make a list of priorities when shopping for a new rifle scope including desired weight, length, elevation and windage adjustments, ballistic turrets, objective lens size, and magnification. Use that list to compare and shop for a scope that best fits all of your wants and needs and completely ignore the tube size. All of those features listed affect the function of the scope, tube size is just a number at the end of the day.