A PADI Open Water card qualifies you to 18 metres. Advanced Open Water raises that to 30. Recreational diving stops at 40 metres, and everything below that line carries a different name and a different syllabus. Three numbers, three sets of reasons.
They are training limits rather than physical barriers. Water does not change at 18.1 metres, and nothing down there reads your card. What changes with depth is arithmetic. Nitrogen loads faster, the cylinder empties faster, and the no-stop clock runs down faster than either. Each rung on the ladder exists because the rung below it did not teach you to manage those three at the next depth.
How deep can an Open Water Diver go?
Eighteen metres, or the depth you reached in training if that was shallower. PADI words it that way on purpose. A diver whose deepest training dive touched 12 metres is qualified to 12, until logged experience and a deeper dive under supervision extend the range.
Age changes the answer. PADI limits junior divers by band, and the supervision requirement comes with it.
- Junior Open Water Diver, ages 10 to 11: a maximum of 12 metres, diving with a PADI Professional or a certified parent or guardian.
- Junior Open Water Diver, ages 12 to 14: 18 metres, still accompanied.
- Open Water Diver, 15 and over: 18 metres with a buddy.
- Advanced Open Water Diver: 30 metres.
- Deep Diver specialty: planning and conducting dives down to 40 metres.
- Past 40 metres: technical training, planned decompression stops and, deeper still, breathing gas that is no longer air.
How deep can an Advanced Open Water Diver go?
Thirty metres. PADI states that an Advanced Open Water Diver is trained to a maximum depth of 30 metres, and the course reaches it through a Deep Adventure Dive under instructor supervision. Underwater Navigation is the other compulsory adventure dive. The pairing is not accidental: at 30 metres you have a fraction of the time to find your way back to the exit.
The Deep Diver specialty goes further and prepares divers to plan dives to 40 metres. Neither certification makes depth safe by itself. What they add is planning, gas reserve discipline and supervised exposure, so the decision to go deep is a considered one rather than a drift downhill. Our Advanced Open Water course runs the Deep and Underwater Navigation dives plus three more of your choosing.
What is a no-decompression limit, and how fast does it shrink?
The no-stop limit is the time you can spend at a given depth and still ascend directly. A safety stop, yes. No obligation to pause at a set depth on the way up. It shortens sharply as you descend. PADI's own figures carry the point: maximum bottom time at 18 metres is 56 minutes, and at 30 metres it is 20 minutes.
Twelve metres of extra depth costs 36 minutes of bottom time. That is the argument against treating a card limit as a target. A 30-metre dive is a short dive by definition. The ascent, the safety stop and the reserve all fit inside a plan that opened with 20 minutes.
Two cautions. A no-stop limit is a computer output, not a number to dive towards. DAN's commentary on no-decompression limits describes error bars on either side of them, with the probability of decompression sickness rising the closer you get. Two divers on the same dive will see different limits if their computers, gas or conservatism settings differ, so the buddy check includes agreeing whose number the team is using. Our guide to decompression sickness covers what the nitrogen is doing while that clock runs down.
How much faster does a cylinder empty at depth?
In direct proportion to ambient pressure. DAN's method is to multiply your surface air consumption rate by the atmospheres of pressure at the planned depth. In metric, pressure is depth divided by ten, plus one. At 18 metres that gives 2.8 atmospheres. At 30 metres, 4. At 40 metres, 5.
Put numbers on it. A diver who would empty a cylinder in 60 minutes at the surface gets about 21 minutes from the same cylinder at 18 metres. At 40 metres the same cylinder lasts 12 minutes. Reserve gas, the ascent and the safety stop all come out of that 12, which leaves a working dive measured in single figures.
This is the part divers underestimate most often, because air consumption feels like a personal trait rather than a depth calculation. It is both. A calm diver at 40 metres still breathes five times the surface volume, and the pressure gauge falls at a rate that looks broken the first time you watch it.
Why is 40 metres the recreational limit?
Three arguments converge there, and none of them is a line painted in the water. The Recreational Scuba Training Council sets 40 metres as the boundary for recreational diving, and the agencies train to it. PADI describes 40 metres as the deepest you can go in recreational diving on air and without decompression stops.
Gas is the first argument. At five atmospheres the cylinder becomes a short-decision device, and the margin for a problem solved at depth shrinks with it. Nitrogen loading is the second. The curve that took bottom time from 56 minutes to 20 keeps bending. A 40-metre air dive is planned around a no-stop allowance with little room for a change of plan.
Narcosis is the third. Reference material on deep diving places the depth at which nitrogen narcosis becomes noticeable in adults at around 30 metres, which is the same depth the Advanced card opens up. Judgement degrades before the diver notices, which is what makes it awkward to self-assess. Our guide to nitrogen narcosis covers the symptoms and the fix.
Oxygen sets the outer wall. Breathing air, the partial pressure of oxygen climbs with depth, and it reaches 1.6 bar at roughly 66 metres, a level treated as an unacceptable risk of oxygen toxicity. Below about 60 metres a hypoxic mix becomes necessary to keep that pressure down. Forty metres sits well inside that wall, with margin left for the diver who goes slightly deeper than planned.
What lies beyond 40 metres?
Different training, not a deeper recreational card. There is no PADI certification that raises a recreational diver past the 40-metre floor, because below it the dives stop being no-stop dives. You accept a decompression obligation, which removes the option of a direct ascent and turns the way up into a scheduled part of the plan.
Gas changes too. Helium displaces some of the nitrogen to keep narcosis manageable, and oxygen content is reduced to keep partial pressures inside limits at depth. Redundant gas supplies, redundant regulators and staged cylinders follow from that, along with the planning to use them. Technical training covers all of it, and it starts in the water well shallower than 40 metres.
For most divers the honest answer sits higher up the ladder. Eighteen metres covers a great deal of what is worth seeing. Thirty covers most of the rest. Divers who get into trouble are rarely the ones who wanted to stay shallow.
Sources
- PADI: How Deep Can Open Water Divers vs. Advanced Open Water Divers Go?. The 18, 30 and 40 metre ladder, the Deep Diver specialty, and the 56 minute and 20 minute bottom times at 18 and 30 metres.
- PADI: PADI Certification Rules Every Diver Should Know. Junior diver depth limits by age band, the supervision requirement, and the wording that an Open Water Diver is limited to training depth if shallower.
- DAN Alert Diver: Estimating Your Air Consumption. The method of multiplying surface air consumption by atmospheres of pressure, and the metric pressure formula.
- DAN Alert Diver: A Critical Look at No-Decompression Limits. Why a no-stop limit is not an absolute safety threshold, and why different computers give different limits.
- Wikipedia: Deep diving. The Recreational Scuba Training Council 40 metre boundary, the depth at which narcosis becomes noticeable, and the oxygen partial pressure figures on air.
- PADI: Advanced Open Water Diver course. The Deep and Underwater Navigation Adventure Dives that make up the core of the course.
Frequently Asked Questions
How deep can an Advanced Open Water Diver go?
Thirty metres. PADI states that an Advanced Open Water Diver is trained to a maximum depth of 30 metres, reached through a supervised Deep Adventure Dive during the course. The Deep Diver specialty extends planning to 40 metres.
How deep can children scuba dive?
Junior Open Water Divers aged 10 to 11 are limited to 12 metres. Ages 12 to 14 may go to 18 metres. Both bands dive accompanied, with a PADI Professional or a certified parent or guardian.
What is the maximum depth for recreational diving?
Forty metres. The Recreational Scuba Training Council sets that boundary and the training agencies work to it. PADI describes 40 metres as the deepest you can go on air without decompression stops.
How long can you stay at 30 metres?
PADI gives a maximum bottom time of 20 minutes at 30 metres, against 56 minutes at 18 metres. Your computer will give its own figure, which varies with the algorithm, the gas and the conservatism setting you have chosen.
How deep can you dive without getting decompression sickness?
There is no depth that removes the risk. Decompression sickness follows from the combination of depth, time and ascent rate, which is why the no-stop limit shortens as depth increases. Staying inside the limit reduces risk rather than eliminating it.
Do you need a course to dive past 30 metres?
Yes, in practice. The Deep Diver specialty is the recreational training that covers planning dives to 40 metres. Past 40 metres there is no deeper recreational certification, only technical training that adds decompression procedures and different breathing gases.
This is general information, not a substitute for a dive medical or advice from a doctor trained in dive medicine. In an emergency, contact your local emergency services and DAN Southern Africa on +27 82 810 6010.
Reviewed September 2026. Devon Ford runs Scuba Evolution, a PADI 5 Star Dive Centre in Glenvista, Johannesburg.
