One atmosphere of pressure appears at 33 feet of seawater, a core fact every open water diver should know

At what depth is one atmosphere of water experienced?

• A. 33 Feet
• B. 66 Feet
• C. 100 Feet
• D. 10 Feet

Answer: (A)

One atmosphere of pressure is experienced at a depth of 33 feet (10 meters) of seawater. This is derived from the understanding that for every 10 meters (or approximately 33 feet) of seawater, the pressure increases by one atmosphere due to the weight of the water above. This concept is essential in diving since divers must be aware of how pressure changes affect their bodies and their equipment. As you descend underwater, the combination of atmospheric pressure and the pressure exerted by the water column above you increases. At sea level, you experience one atmosphere of pressure from the air surrounding you. When you go down to a depth of 33 feet, you add another atmosphere from the seawater, resulting in a total pressure of two atmospheres. This foundational knowledge is crucial for safe diving practices, including understanding the impacts on buoyancy, breathing gas expansion, and potential risks like decompression sickness.

Let’s start with a simple, almost blue-print idea that every diver learns early: depth and pressure aren’t distant cousins. They’re partners. As you go under the surface, pressure stacks up like layers in a parfait you didn’t order but somehow really need. The key fact is surprisingly clean: one atmosphere of pressure is experienced at about 33 feet (10 meters) of seawater. In other words, at 33 feet down, you’re carrying two atmospheres of pressure—one from the air around you and one from the water above you.

Let me explain why that number sticks in your head. It’s not magic. It’s a straightforward consequence of how water weighs on whatever is below it. Air at sea level presses on you with one atmosphere of pressure. Add water on top, and the pressure from that water column increases by roughly one atmosphere for every 10 meters you descend. So the math is simple, even when the environment isn’t: surface = 1 atm, at 10 meters = 2 atm, at 20 meters = 3 atm, and so on. The 33-foot benchmark—about 10 meters—is where the water’s weight adds that second atmosphere.

Why should you care about that simple rule? Because it changes more than the number on a gauge. It affects the whole experience of being underwater: how you breathe, how your buoyancy behaves, how your gear feels, and even how your body responds to movement.

Breathing and gas dynamics (the practical bit)

Breathing air at depth isn’t the same as breathing on land. The air you receive from a regulator is delivered at ambient pressure—that is, the pressure that exists in the water around you. Since pressure goes up with depth, the gas in your lungs is compressed as you descend. The regulator does the heavy lifting, reducing the water’s pressure to a breathable mix, but you still feel the changes inside you.

That pressure compression has consequences. If you carry a fixed amount of gas in your tanks, a change in depth changes how much gas you have available at any moment. Descents can feel effortless at first, but as you go deeper, your gas pool is used at a different rate relative to your buoyant state. It’s a delicate balance: more pressure means smaller gas volume in the tank bumping around your lungs, but the regulator keeps that gas flowing as needed. The result is something you learn through feel, almost like your body adjusts its own internal “fuel gauge” as you move.

A practical way to picture this is to imagine a sponge soaking up water. When you’re shallow, the water pressure is lighter and your lungs fill more readily. As you descend, the surrounding pressure pushes the gas in your lungs more tightly, and your own breathing pattern may change to keep things comfortable. It’s not about becoming tense; it’s about listening to your body and letting your training guide your actions—steady breaths, calm movements, and smart gas planning.

Buoyancy and the gear dance

Buoyancy control is the art of staying where you want to be in the water column without fighting against yourself all the time. Pressure has a surprising role here too. The neoprene suit you wear compresses as you descend, which changes your buoyancy slightly. The same thing happens with air in the buoyancy compensator (BC) and, to a lesser extent, your lungs. If you ignore these shifts, you’ll notice yourself drifting up or down a bit more than you expected.

That’s why a careful, gradual descent is drilled into every Open Water curriculum. You’re not just moving through space; you’re orchestrating a balance between weight, buoyancy, and the pressure that’s everywhere around you. A quick, practical takeaway: check your buoyancy after reaching a new depth, and make minor adjustments slowly. It’s not flashy, but it’s how you stay in control when the water doesn’t care about your plans.

Decompression and safety reminders

As pressure rises with depth, dissolved gases in your tissues behave differently. The most important safety note is simple: rising too fast can cause inert gases to come out of solution and form bubbles in your body. That’s the core of decompression concerns. It’s not a fear tactic; it’s physics meeting physiology, and it’s why ascent profiles, safety stops, and proper flights home (if you’re traveling after a dive) matter so much.

You don’t have to memorize heavy tables to be mindful. The essential habits are clear:

• Plan your depth and time, then follow a conservative ascent.

• Keep your movements smooth; avoid rapid changes in depth.

• Breathe steadily, never hold your breath, and give your body time to adjust to depth changes.

If you’ve ever felt a pressure “pinch” in your ears on a descent, you know how real this is. It’s a reminder that your body is connected to the depth you’re exploring, and that connection has rules you respect to stay out of trouble.

A mental model you can carry with you

Here’s a simple way to remember the core idea without getting lost in numbers:

• Surface pressure is one atmosphere.

• For every 10 meters (approximately 33 feet) you go down, you add roughly one atmosphere of pressure from the water column.

• That means at 33 feet you’re at about two atmospheres total, at 66 feet you’re around three atmospheres, and so on.

Keep this model in your pocket when you’re planning a dive. It’s not just about satisfying curiosity; it’s about safety and confidence. When you understand that pressure changes with depth, you start to see why buoyancy, gas management, and controlled movement aren’t separate skills—they’re part of a single, coherent system.

A few analogies to keep things relatable

If you’ve ever ridden an elevator, you know how different floors feel. The water pressure at depth is a slow, constant lift you don’t notice in the moment, but it’s there—pushing, compressing, shaping every action you take. Or think of your lungs as a flexible balloon that responds to the weight of the water above you. As you descend, the surrounding pressure nudges the gas in that balloon a bit tighter; as you ascend, the balloon wants to expand. Your job is to manage that expansion and contraction gracefully, not to fight it.

A note on the broader picture

Open water training isn’t just about hitting a number on a depth gauge. It’s about how you apply that knowledge to real-world scenarios: choosing a comfortable depth for a given day, recognizing how your equipment behaves under pressure, and keeping a calm approach even when currents or visibility shift. The depth-and-pressure principle is the bedrock that links all those skills. It gives you a reliable framework to make smart choices beneath the surface.

A quick glance at the tools you’ll notice in practice

• A depth gauge and a bottom timer or computer help you track how long you’ve been down at a given depth.

• Your regulator and tank system are designed to deliver air at ambient pressure, which is why the depth you’re at matters for how you breathe.

• The buoyancy control device (BCD) helps you adjust your position in the water column as pressure changes, so you stay level without fighting gravity.

If you’re curious about the science behind it, several reputable sources and training materials from established dive programs walk through the same ideas with diagrams and real-world examples. The essential point stays the same: depth and pressure are interlocked, and understanding that link makes every dive safer and more enjoyable.

Putting it all together in the water

As you move through an Open Water curriculum, you’ll practice these concepts in controlled steps. You’ll feel the difference as you descend from the surface and notice how your breathing, buoyancy, and comfort level adjust. You’ll experience that moment when the water becomes a shade darker, your ears acclimate, and your mind shifts into a steady, methodical pace. That’s not magic; that’s training meeting reality.

Let me leave you with a practical takeaway you can carry forward

• Remember the 33-foot rule as a mental anchor.

• Use it to anticipate how your equipment and body will respond as you adjust depth.

• Practice gentle, planned movements to keep buoyancy stable.

• Keep your breathing calm and consistent; it’s your best ally against surprises.

So next time you’re near the surface and you imagine what life is like a few feet below, picture that first 33 feet and the moment your surroundings merge with a second atmosphere. It’s a small distance, but it carries a big idea: in water, pressure isn’t a villain—it’s a constant, guiding companion that helps you move with purpose, stay safe, and enjoy every moment of your underwater journey.