What Are the Different Lengths of AR 15 Uppers?

There are several ways to measure the length of an AR 15. Some prefer to classify length by the gas system. Others use the barrel length. Still, others prefer to organize length by AR 15 upper assembly length or overall rifle length. We will discuss all the different ways to measure an AR 15 and review the benefits and drawbacks of each length.

There is no best length for every circumstance; that’s why many different sizes exist. Depending on what you need to accomplish, there is a best length for each task. We are going to look at the most common measurements and what they are best suited for.

We are only going to go to different lengths. We will not be going over caliber, affecting the weapon's performance.

How to Measure an AR 15 Length

One of the first things to consider when looking at the length of an AR-15 Upper is to decide if you have a rifle or pistol. Because different components qualify a weapon as a pistol or rifle. One of the first things to consider is the stock. The stock is only one feature defining a weapon as a pistol or rifle. So, if you have what might otherwise be categorized as a pistol but install a rifle stock onto it, it would be recategorized as a short-barreled rifle.

Once you know what type of weapon you are measuring, it is a good idea to understand why you want to measure it. To ensure it will fit into a safe or carry bag, you will want to know the overall length. You will likely want someone certified to look at it if it is for legal reasons.

That being said, it is relatively easy to measure the components of your AR 15 if you are curious about the measurements. Below, we will take a closer look at how to identify and measure each of the different ways to measure your AR 15.

Gas System Length Explained

The Gas system on an AR 15 is one of the easiest ways to identify. The lengths are different enough that they are generally identifiable just by sight. The gas system is located on the top of the barrel, typically under the handguard. It sends gas from the expended round back to the BCG, allowing the spent round to be expelled and the new round loaded.

If the gas system is too short, it will return too much gas to the receiver. This creates more significant recoil that wears parts out faster. Shorter gas systems must be accounted for with adjustable gas blocks and heavier buffers.

If the gas system is too long, it will not send enough gas back to allow the BCG to operate correctly. This means the rifle may jam without the proper force applied to the BCG to extract and chamber the rounds.

There are four standard gas system lengths.

Pistol Length:

The shortest is pistol length. The average length for a pistol-length gas system is 4.5 inches. This provides for a high-speed and heavy cycle. Creating increased recoil, so rapid follow-up shots tend to be less accurate. It may also require a muzzle device with heavy upward gas deflection to decrease muzzle rise. This is the length of a gas system for very short barrels, such as 7.5-inch barrels.

Carbine Length:

A carbine-length gas system is the most common gas system; the tube is about 7.5 inches long. This system works best with barrels between 10-18 inches long. For a barrel that is 10 inches long, the carbine length is a good choice, even though you can still get a 10-inch barrel with a pistol-length gas system.

Mid-length:

A mid-length gas system is slightly longer than a carbine length and measures about 9.5 inches. Rifle with longer barrels in the 14–20-inch length performs better with mid-length gas systems.

Rifle Length:

A rifle-length gas system is the most extended system at about 13 inches long. A rifle-length gas system is best for rifles with 20-inch or longer barrels. This includes barrels of 24 inches as well. These are used primarily for sharpshooters who want to shoot longer distances. 

Barrel Length Explained

The following common way to measure the length of an AR 15 is to use the barrel length. You'll be able to read this to learn how to measure barrel length precisely. But overall, you know the general length of your barrel. This is an excellent way to describe to yourself or others how long your AR 15 is. If you say you have a 16-inch AR 15, most everyone understands you have a 16-inch barreled AR 15.

If you have an AR 15 with any barrel shorter than 16 inches, you risk it being defined as a pistol or AOW. So, the rule of thumb is to be sure you have a 16” barrel if you want a rifle. Barrels are commonly sold commercially from 7.5 to 20 inches, with 16 inches being the most common.

The longer the barrel, the more accurate it is at farther distances it can fire. I suggest fire because it still depends on other factors, such as what rifling, caliber, and sights are used. Also, what are the altitude and weather conditions when using?

Remember to check the location of the gas port on the barrel when measuring it for length, especially if you are tuning your weapon. A more extended gas system will often be required as barrel length increases.

An AR-15 platform weapon can often be customized to meet many length requirements. That is one of many of the wide range of features of an AR 15.

Upper Assembly Length Explained

Another way to measure the length of your AR 15 is to measure the overall upper assembly. The reason for measuring this way might be because you are separating the upper and lower sections for more straightforward transporting and want to buy a proper carry bag, chest, or box. The way to measure this would be to remove the upper assembly from the lower body and measure the upper from the muzzle device to the rear of the upper receiver or charging handle if left in. This will typically be the longest section of the rifle when separated.

This measurement can vary significantly from upper to upper. So, if you are curious, use a tape measurer or yardstick to get the overall length of your upper receiver.

Overall AR 15 Length Explained

The overall length of your AR 15 is easy to measure. If you have a collapsible stock, put it in the shortest position. Then, measure from the stock to the muzzle device. This will give you the overall length of your AR 15. This measurement may be helpful if you are going to use a mount. It will also be vital if you are shopping for gun safes or carry bags.

Sometimes, as little as ½ an inch may make all the difference between fitting or not fitting. The easiest way to change the overall length of your rifle is to change the stock. There are a multitude of different stocks to choose from. Stocks come in oversized, extended, standard, and compact. So, determine what you need and shop accordingly.

Shopping for AR 15 Parts

If you are clear on the length of rifle or pistol you want for your next AR 15 build and enjoy the best prices and selection on AR 15 Parts, shop now at Black Rifle Depot. With live inventory and five-star customer service, you can shop happily. Explore the AR 15 Products with various options, including bolt carrier groups, free float handguards, stocks, barrels, and grips.