How Deep Can You Dive? Depth Limits in Meters and Feet

The short answer

Recreational scuba stops at 40 m (130 ft). Trained technical divers using mixed gases work to 100 m (328 ft) and beyond, with the record scuba descent standing at 332.35 m (1,090 ft). Commercial saturation divers have worked at 534 m (1,752 ft) in the open sea. Crewed submersibles have reached the bottom of the ocean at 10,935 m (35,876 ft).

Each of those limits exists for a different physical reason. Recreational scuba is limited by gas narcosis and air supply, technical diving by oxygen toxicity and decompression obligation, saturation diving by high-pressure nervous syndrome, and submersibles only by the engineering of a pressure hull.

Pressure is the whole story

Water is about 800 times denser than air, so depth accumulates pressure fast:

That final column is the practical constraint on recreational diving. A tank that gives 60 minutes at the surface gives 12 minutes at 40 m. Add the reserve every diver should surface with and the usable bottom time collapses.

The precise figure is one atmosphere per 10.06 m of seawater, which is why dive tables and computers built for freshwater read slightly differently from saltwater ones. Freshwater is less dense, so a freshwater atmosphere is 10.33 m.

Recreational scuba: the 40 m ceiling

Every major agency, including PADI, SSI, NAUI, and CMAS, treats 40 m as the outer boundary of recreational diving. Below that you are in technical diving, with different training, gases, and equipment.

Three things go wrong at once at 40 m.

Nitrogen narcosis. Under pressure, nitrogen dissolves into nerve tissue and produces effects comparable to alcohol. The old rule of thumb is that every 15 m below 20 m feels like one martini on an empty stomach. Most divers notice it around 30 m, and by 40 m a meaningful fraction of divers show impaired judgment and slowed reaction time. The dangerous part is that narcosis degrades the very faculty you would use to notice it.

No-decompression time. At 18 m a diver has roughly 56 minutes before mandatory decompression stops. At 40 m that falls to about 8 minutes. Beyond it, any dive of useful length carries a decompression obligation, which means you can no longer ascend directly to the surface in an emergency.

Oxygen partial pressure. Breathing air at 40 m puts oxygen at 1.05 bar partial pressure. The accepted working ceiling is 1.4 bar, reached on air at about 56 m, with 1.6 bar as an absolute contingency limit. Past that, central nervous system oxygen toxicity becomes a real risk, and an oxygen seizure underwater is almost always fatal.

Technical diving and the scuba record

Technical divers get past those limits by changing the gas. Trimix replaces some nitrogen with helium, which is far less narcotic and keeps the oxygen fraction low enough to stay under 1.4 bar at depth. The cost is a longer, more complex decompression and an expensive gas bill.

Ahmed Gabr’s 332.35 m dive off Dahab in September 2014 remains the deepest scuba descent recorded. The asymmetry of that dive is the striking part: about 12 minutes down, and roughly 13 hours and 35 minutes coming back up. Below about 150 m the ascent is the dive.

Freediving numbers look implausible next to these until you remember that a freediver carries no gas and therefore accumulates almost no dissolved nitrogen. Herbert Nitsch reached 214 m (702 ft) in the No Limits discipline in 2007, riding a weighted sled down and a lift bag up. In Constant Weight, where the diver swims down and back under their own power, the record sits at 136 m (446 ft).

Commercial and military depths

Saturation diving takes a different approach again: keep the diver at working pressure continuously for weeks in a pressurized habitat, so decompression happens once at the end rather than after every shift.

The barrier for humans in the water is high-pressure nervous syndrome, a tremor and cognitive disturbance that appears in helium-oxygen breathing below roughly 150 m and worsens with depth and compression rate. Comex managed 701 m in a chamber by adding a small nitrogen fraction to the mix and compressing very slowly. That figure has stood since 1992 and is generally treated as near the physiological ceiling.

Altitude, freshwater, and flying afterwards

Depth limits assume you are diving at sea level in salt water. Change either variable and the numbers move.

Altitude diving starts at 300 m (984 ft) of surface elevation, the threshold at which every agency requires adjusted tables. The surrounding air pressure is lower, so the pressure gradient a diver ascends into is steeper than the tables assume, and the effective decompression obligation is larger than the depth gauge suggests. A 30 m dive in Lake Tahoe at 1,897 m elevation carries roughly the decompression penalty of a 40 m dive at sea level. Depth gauges calibrated for salt water also over-read in fresh water by about 3 percent, which happens to work in the diver’s favor.

Flying after diving is the reverse problem. Airliner cabins are pressurized to an equivalent altitude of 1,800 to 2,400 m, so boarding a flight is a further ascent. Divers Alert Network guidance is a minimum 12-hour surface interval after a single no-decompression dive, 18 hours after multiple dives or multiple days of diving, and substantially longer after any dive requiring decompression stops. The same caution applies to driving over a mountain pass, which is the overlooked version of this rule and the reason dive operators in Central America ask where you are headed next.

Below the divers: the ocean’s own depths

Past 1,000 m no human enters the water directly. Everything deeper is done inside a pressure hull.

The Challenger Deep figure is worth pausing on. At 10,935 m the pressure is about 1,090 atmospheres, more than a tonne per square centimeter. Mount Everest, at 8,848.86 m, would sit entirely inside the trench with over 2 km of water still above its summit. Our guide to mountain elevation in feet and meters covers the surface half of that comparison, including why summit elevations get revised.

For scale in the other direction, an Olympic swimming pool is 2 to 3 m deep, which is one three-thousandth of the way to the bottom of the Mariana Trench. The meters-to-feet calculator handles any depth in this guide, and the conversion worth memorizing is the simplest one in diving: 10 m of seawater is 33 ft and one extra atmosphere, every single time.

Sources and further reading:

• NOAA Ocean Exploration: Technical diving
• NOAA Ocean Service: How deep is the ocean?
• Scuba Diving: Why is 130 feet the depth limit for recreational scuba?
• Wikipedia: Challenger Deep
• Wikipedia: Deep diving
• Our guide: Mountain elevation: feet vs meters