Ambient Air

What Diameter of Ducting Do I Need?

Urethane Flex Heavy Duty

When it comes to ducting, it is sometimes hard to tell what diameter of ducting you need. There are many options available to you. And the choices can feel overwhelming. What does duct size mean, anyway? Duct size simply refers to the diameter of a given hose. Some hoses have diameters that are as small as an inch. Others have diameters that are as large as 5 feet! Applications such as industrial factories, agricultural operations, and street sweeping often require large ductwork—a large hose can accommodate the large amounts of mass that these applications tend to transport at once. Factories, for example, may need to exhaust large volumes of fumes at high rates, requiring the need for a large hose. Coupled with the fact that you can get your ductwork’s diameter customized, too—it makes sense to wonder about which diameter of ducting you need for your project. What diameter hose is best? It depends on the application toward which you intend to apply the hose. But what if you get the wrong size? What happens if you oversize duct-work? And what happens if ducts are too small? Whether you need an extra-large hose or something much smaller, this comprehensive guide will walk you through the basics of how ductwork is sized. The diameter of ductwork is a subject that is often overcomplicated. It really is quite simple. First off, what does duct size mean?

Air Ventilator Heavy Duty Ventilation Hose

Temperature Range: -20°F to +180°F Sizes I.D. (in.): 6, 8, 12, 14, 16, & 24

Thermoplastic Flex Medium-Duty WS Thermoplastic Rubber Duct

Temperature Range: -40°F to 275°F. Sizes I.D. (in.): 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, & 24

Tornado Flex Flexible Air Ducting

Lead Time 4-6 Weeks Temperature Range: -20°F to +180°F Sizes I.D. (in.): 4, 5, 6, 7, 8, 10, 12, 14, 16, 18, 20, & 24

Wind Handler Insulated TU Insulated Ducting

Lead Time 4-6 Weeks Temperature Range: -40°F to +250°F Sizes I.D. (in.): 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, & 24

What Does Duct Size Mean?

Duct size refers to the diameter of ductwork. A duct’s diameter is expressed as its ID, or inside diameter. This measurement excludes the thickness of the hose’s walls. Hoses are designed to attach to hollow, cylindrical openings. These openings are protrusions over which the hose’s mouth fits. Because ducting applications are designed this way, pipes, connectors, or other openings to which ducts will attach are measured in terms of OD, or outside diameter. An object’s outside diameter is a measurement of its diameter that includes the thickness of its walls. Vents, exhausts, and other openings meant for ducts are measured in terms of their ODs so that a hoses will actually be able to fit over the openings. If these openings were measured in terms of ID, too, then an opening and a duct with the same ID-size would not connect, as the thicknesses of their walls would prevent one object from fitting over the other. This is why it has become standard for hoses to fit over the objects to which they connect. Keeping this process uniform minimizes the amount of confusion consumers must undergo to purchase the right-sized hose. As well, matching the OD of a connector with the ID size of a hose makes things simpler, as buyers will not have to balance as many numbers in their heads as they look for new hoses. Now that you know how ducts are sized—what about when you want to know what is the diameter of a hose?

What Is the Diameter of a Hose?

The diameter of a hose is its inside diameter, or its diameter excluding the thickness of its walls. How do I know my hose size? To find the diameter of a hose, hold the hose up to you—in such a way that its mouth is facing you. Using measuring tape, measure the diameter of this opening from the beginning of one interior wall to the beginning of the interior wall that is directly opposite to the former wall. (You may use a ruler to accomplish this, but for a large hose, you may have to use measuring tape.) This is one way of obtaining the inside diameter of a hose. You can also measure the total diameter of the hose’s mouth. Then, take the thickness of the hose’s walls—either by knowing it beforehand or measuring it yourself—multiply it by two, then subtracting this value from the total diameter of the hose’s mouth. This is another way of calculating your hose’s inside-diameter.

While both methods are equally effective at deriving a hose’s inside-diameter, you may want to do them both. This way, if you reach the same value using two different methods, you can be more certain that the ID size you concluded is accurate. And if one of them gives you a value that differs from the value yielded by the other method, this is a good indicator that you should retrace your steps and remeasure your hose. After all, you want to make sure you correctly measure your hose’s inside-diameter. It is certainly worth the extra time!

Neoprene Flex 2 Ply WS_Flex Shot

What Happens If Ducts Are Too Small?

If ducts are too small, they likely will not fit over the openings to which you intend to attach them. In these cases, ductwork may only fit over a connector if the difference between the duct’s ID and the connector’s OD is within the duct’s ID-tolerance range. Generally, this can only happen if the difference between the duct’s ID and the opening’s OD is very slight. For the most part, undersized ductwork is highly undesirable, as it will lead to—at best—a poorly-functioning system. When ductwork is too small for the amount of material that you intend to transfer through it, the duct certainly will not be able to deliver the volume you want it to at the rate you want it to. The hose simply is not wide enough to carry that much mass at once. In some cases, ducts can be so undersized that the amount of outward pressure from within the hose can cause the hose to explode. This is especially common for air ventilation applications that use hoses that are too small. Now, you might think that these problems do not apply to, say, a large air duct since it is such a large hose that under-sizing is not an issue. However, the same principles apply to large, flexible ducting, too. A large duct can encounter similar issues—they just happen with larger masses of materials or air. Thus, regardless of whether you have a small- or large-diameter hose, it is important to make sure your duct is not too small for your application.

What Happens If You Oversize Duct-work?

When you oversize ductwork, you risk making the connection between the duct and your machinery insecure, drastically decreasing the efficiency of your system. While oversized ductwork tends to be an issue, this does not mean that products such as a large-diameter hose are inherently bad. It just means that you must be diligent when choosing the size of your duct.

Air Ventilator Black_Flex Shot

A large hose is highly useful in a variety of settings, and the accuracy of the IDs of large ductwork is just as important as that of the IDs of small ductwork. Nonetheless, there are outlier scenarios where the positive difference between your duct’s ID-size and a connector’s OD-size is so small that you can stuff the hose’s end into the opening without affecting the system’s efficiency. But, as we have said, these are rare cases. Oversized ducting is much harder to work around than undersized ducting is.

What Diameter Hose Is Best?

The hose diameter that is best for you depends on your application. For example, material-transfer applications—such as street sweepers, farm machinery, and industrial factories—all rely on large ductwork. A large-diameter hose is wide enough to carry many of the materials that these applications handle, and using a large hose also allows large volumes of materials to be transported at once. There are even applications that require a 60-inch-wide hose! Thus, some applications demand large-diameter, flexible ducting, whereas others may simply call for a smaller hose. Large hoses mainly offer the advantage that they can carry drastically larger amounts of material or air at once. After all, the larger the hose, the more you can fit into it at a time. The problem, though, is that many users underestimate the quantity of material their application transfers at once. That is, they tend to underestimate the volume of material or air that will be transferred and the rate at which that volume will be pushed through the hose. This often leads to large ductwork that is nonetheless too small for the application for which a customer purchased it. This is of especial concern for those who are looking to ventilate large quantities of air, as ductwork that is too small for the volume of air it transports has a strong likelihood of puncturing. The hoses within our Air Ventilator series are perfect examples of large-diameter, flexible ducting that is made to handle extremely large quantities of air at once. These hoses can be made in ID sizes of up to 60 inches! They are made of a highly durable, PVC-coated fabric. This PVC coating gives the hose an incredible amount of resistance to abrasion, both within and outside the house. Furthermore, the hose’s fabric material makes it highly compressible, as well as flexible. In fact, our Air Ventilator Black duct has a 9-to-1 compression ratio. This means that an 18-feet-long section of hosing can compression down to 2 feet! This makes any hose within our Air Ventilator series highly transportable—perfect for air-transfer applications that are on the go! Of course, even a large hose in this series is easy to transport.

Thus, heavy-duty air-ventilation applications that need to be mobile can greatly benefit from the implementation of a large-diameter hose such as the Air Ventilator Black from This hose works great for both indoor and outdoor applications, as its external wear-strip protects it from sustaining damage as you drag it across the ground. The steel-wire helix that spirals throughout the hose’s body ensures that the hose remains highly crush-resistant. Of course, this hose is just one example of the many large-diameter hoses available at Each of which offers a unique profile of properties that accommodates a different application.

Review: How Do I Know My Hose Size?

To know your hose size, measure the inside diameter, or ID, of your hose. This is the measurement of the hose’s diameter, excluding the thickness of the hose’s walls. ID size is the industry-wide standard for expressing a duct’s width, and it helps optimize buyers’ experiences when they look for a hose. As we have mentioned, there are a few ways for you to find out the size of your hose. For one thing, the specifications sheet that came with your hose may contain information regarding the item’s ID size. If you need to measure your hose’s ID size yourself, though, the processes available to you are simple. One of the easiest ways to measure the ID size of your hose is to use measuring tape to calculate the inside diameter of the hose. Remember to exclude the thickness of the hose’s walls from your measurement, as including this value will quickly hinder the application for which you intend to use the hose. You can also just take the hose’s total diameter, including the thickness of its walls. Then, separately measure how thick the hose’s walls are, multiply this value by two, then subtract this number from the total diameter you gathered earlier. While this process involves more steps, it may be helpful in addition to the first method if you wish to obtain your hose’s ID size using two different methods—reaching the same result through multiple processes enhances its veracity.

Neoprene Flex 1 Ply_Flex Shot

All in all, when looking for the right diameter of ducting for your application, keep in mind that hoses sizes are measured in terms of inside diameter and that the right size of hosing depends on your application. While there are some instances wherein variations from the proper ID-size are acceptable, these are generally uncommon. Even when dealing with an application that demands a large hose, the same principles apply. How your hose is sized and how you should go about measuring its size remain consistent, even as you reach the upper limits of ID size.