Scuba diving and exploring the endless depths of the ocean is one of the most rewarding activities one can do. You will also meet some amazing people along the way who’ll be by your side as you head into the depths. However, those looking from the outside and seeing all of the gear required to scuba safely will feel intimidated. At a very basic level, they are wondering if they can even carry and swim with all of that gear.
Out of all the equipment in a diver’s kit, the scuba tank is the heaviest and arguably the single most important piece of gear in the setup. A typical scuba cylinder weighs 26 to 40 pounds out of the water. In general, aluminum tanks are heavier than steel tanks. In the water, however, all tanks regardless of material will be mostly weightless.
How heavy a scuba tank is and how encumbering it is to wear depends on various factors. The most important factor is the size of the tank and how long you plan on diving for. You should not be overly concerned with how heavy a tank is on land. In the water, you will barely feel the weight. Furthermore, with sufficient physical training and guidance under a knowledgeable instructor, you will be able to scuba dive well. Below are some of the things a scuba instructor will teach you about scuba tanks.
Types of Scuba Tanks
The two most popular types of scuba tanks are steel and aluminum tanks. As we mentioned above, aluminum tanks are heavier than steel tanks which doesn’t seem right. After all, aluminum is the lighter material. If you’ve ever held an empty soda can in your hand, you’ll notice it feels light and you could easily crush it, so it’s not very durable either.
On the other hand, steel is 2.5 times denser than aluminum, so technically it is the heavier material. However, the strength of metal is why steel tanks are lighter. The walls of a steel tank do not need to be as thick so less material is used. This means that despite being the heavier material, steel tanks are lighter than aluminum tanks.
Since aluminum is not as strong as steel, aluminum tanks have to be much thicker to compensate. This has two downsides. One is that the extra aluminum makes the tanks heavier. The second is that since the cylinder walls are thicker, it holds less air than steel tanks.
Furthermore, steel tanks come in various sizes. Most are around two and a half feet long and weigh about 26 to 40 pounds, but the largest tanks are even bigger and heavier than this. A larger tank will also have greater air capacity, letting divers have longer bottom times. However, larger tanks cost more to fill.
Weight on Land
The weight of a scuba tank on land is referred to scuba divers as the “dry weight.” The dry weight of steel tanks is around 26-30 lbs, and aluminum tanks generally weigh within 31-35 pounds.
Unsure of how heavy 35 lbs is? That’s about the weight of a 4-year old child. If you have a young nephew or niece or a child of your own to pick up or give a piggyback ride to, then you will have an idea of how heavy an aluminum cylinder is. Another way to get a feel for 35 lbs is to get a backpack and fill it with heavy textbooks. A scuba tank will probably be a little heavier than that. And that’s just the weight of the scuba tank without factoring in the weight from the rest of your gear.
If you find that carrying this much weight briefly is exhausting, then you could benefit from doing some physical training. With that said, you don’t need to carry all of this weight for very long; just the short period of time from when you wear it on the boat or shore to when you dive into the water. Once submerged, suddenly all of that heavy gear will feel weightless and you won’t feel as encumbered.
Furthermore, the average adult should be capable of carrying a tank with almost no effort. In fact, it’s more important to focus on training your cardiovascular system (heart and lungs) so that you can be more efficient in your air consumption and not fatigue so quickly when swimming.
Carrying on from above, once you’re in the water, you will feel almost weightless. The reason why this occurs is thanks to buoyancy, which is when liquid pushes up on an object. Sometimes this force is greater than the object’s weight, and it causes the object to float up. This is known as positive buoyancy. Sometimes the force isn’t strong enough and the object sinks; this is negative buoyancy. Lastly, when the weight of the object and the force acting on it is equal, neutral buoyancy is achieved.
When one is neutrally buoyant, one is neither ascending nor descending; they are simply floating in place. By using your buoyancy control device (BCD), you can adjust your buoyancy so that you are floating in place as if you weighed nothing. The BCD is arguably as important as the scuba tank itself because it controls whether you are sinking, floating, or staying in place.
Achieving neutral buoyancy is a delicate balancing act. Your body doesn’t actually weigh less underwater; because of buoyancy, water is pushing against your weight as well as the weight of your scuba gear. If you are negatively buoyant with all of your gear, you need to be sure that the BCD can support your weight. Since the air in your lungs as well as the air bubbles in your neoprene equipment provide plenty of positive buoyancy naturally, your BCD doesn’t have to work as hard to keep you afloat.
Lastly, keep in mind the buoyancy of a steel tank vs. an aluminum tank. A full steel tank will be negatively buoyant underwater. Even as it empties, it will become slightly less negatively buoyant but will still have negative buoyancy overall. On the other hand, an aluminum tank will be negatively buoyant when full, but as it empties it will eventually become positively buoyant.
Full vs. Empty Scuba Tank Weight
Did you know that air has mass? Air weighs approximately 1.3g per liter. So if you know how many liters of volume your tank has and factor its maximum fill pressure, then you can approximately calculate the weight of compressed air in an empty vs. full tank. Of course, this also means that a smaller tank which holds less air will not be as heavy as a larger tank that can hold more air. For instance, a full 80 cf tank will hold approximately 6 lbs of air. A full 120 cf tank will hold approximately 9 lbs of air.
You don’t have to do this calculation yourself. Most manufacturers have already listed the empty, full, and minimal pressure (usually 500 psi) weight of the tank. This measurement typically excludes the weight of the valve. So if a typical tank weighs 26 to 40 lbs, add another 6 to 9 lbs to get the weight of a full tank.
However, divers almost never use up all of the air in their tanks. Once your submersible pressure gauge (SPG) starts pointing to the red, it’s about time to make your ascent. Furthermore, for storage purposes tanks are never left completely full or empty either. This means the weight of the tank with approximately 500 psi of air is probably the most accurate weight of an “empty” tank.
Air Composition and Weight
Another common question divers have is how Nitrox factors into the weight discussion. After all, Nitrox is made up of higher oxygen content, often between 22 to 40% compared to 21% in normal air. Does this difference in mixture affect how much it weighs?
If you consider that nitrogen is 3% lighter than oxygen, technically Nitrox will weigh more than regular compressed air. Whether you did the math or you just lifted up a tank with a Nitrox mix and compared it to one without, you’ll realize that the difference in weight is negligible. It’s much easier to just assume each mixture weighs the same.
Carrying Heavy Tanks with Injuries or Disabilities
If you have a serious injury or disability but still wish to scuba dive, you should first consult with your doctor and a dive instructor and get a thumbs up from both of them before diving. After all, how can you carry a heavy scuba tank and other equipment if you have a chronic back injury for example?
Thankfully, as we mentioned above, you do not need to carry the weight for long. Once you make it in the water, the buoyancy provided by the water should provide some relief from your back pain.
If your condition makes it difficult for you to carry heavy gear above water, particularly when surfacing, then let your instructor and diving partner(s) know. They can figure out a way to help you handle the gear out of the water.
Furthermore, you don’t even need to wear your gear above water at all. You can get in the water first and have someone hand you each piece of equipment as you equip it. Do the reverse process when it is time to get back on the boat by taking off each piece one by one and handing it to someone on the boat.
The diving community has some of the most supportive people in the world. They are always eager to provide advice and assistance to those who need it. There are even organizations formed specifically to assist divers with disabilities, such as Disabled Divers International and Handicapped Scuba Association. So if your disability is currently holding you back from diving; know that help is out there.
Selecting a Scuba Cylinder
Unless you are doing deep or technical diving, there’s no need for you to get a large and heavy scuba cylinder. You can always go for a smaller, lighter model with less air capacity. If you are on the smaller side or just want a lighter tank, you should consider investing in a lightweight steel tank. Unfortunately, steel tanks are more expensive so if cost is a concern then you have no choice but to get a heavier aluminum tank. If you dive locally, then it makes sense to invest in a tank of your own.
If you travel by air to your scuba destination, then you will probably end up renting a tank. When renting, there are always sanitation concerns, particularly in a world ravaged by COVID-19. However, don’t fret. No one is exhaling into the tank; it’s your regulator and mouthpiece that should be a concern. Dive shops are hopefully doing a thorough job disinfecting each tank so that it’s safe for the next diver.
Standard scuba tanks that you can rent/purchase are 80 cf aluminum tanks with a maximum fill pressure of 3,000 psi (207 bar). An equivalent steel tank will be a few pounds lighter. You can read more about the best scuba tanks in our comprehensive review and buying guide.