Open Water Diver: what you can do, what you learn, how it’s tested
In short
Open Water Diver is the entry-level scuba certification: you and a certified buddy can plan your own dives. With PADI, you can start at 10, and adult Open Water Divers stay above about 18 m (60 ft). The theory covers gear, pressure, buddy procedures, emergencies and dive planning, and the knowledge part ends with a final exam.
On your first open water dive, your ears push back a few meters (feet) down. Your gauge drops faster than it did in the pool. Then you look around and your buddy is gone. Each of these moments has a rule behind it, and you learn the rules on dry land before the final exam. This page covers the certification’s limits, the theory and how to study it.
What does an Open Water Diver certification let you do?
It lets you plan and make your own dives with a certified buddy, without an instructor, within the limits of your training. You can rent gear, get your tank filled and book dives with dive centers. It’s also the starting point for every further course, from Advanced Open Water to Divemaster.
Your training also sets where you can dive: stay in conditions similar to, or better than, the ones you trained in. A cold, dark lake or a strong current is a different dive from a calm tropical reef: go with a professional the first time, or take more training. Caves, wreck interiors and dives that need decompression stops all require specific courses.
The figures below come from the public pages of the PADI Open Water Diver course, read on November 11, 2026. Octo is an unofficial app, not affiliated with or endorsed by PADI. Other agencies, such as SSI, NAUI or CMAS, run similar but not identical entry-level courses, with their own ages, limits and names.
How deep can an Open Water Diver go?
About 18 m (60 ft) for adults. The certification FAQ says beginning divers stay shallower than about 18 m (60 ft), and the published restrictions set the same maximum for adult Open Water Divers. Junior divers have extra limits.
| Diver | Maximum depth | Who you dive with |
|---|---|---|
| Junior, aged 10 or 11 | 12 m (40 ft) | A dive professional, or a certified parent or guardian |
| Junior, aged 12 to 14 | 18 m (60 ft) | A certified adult |
| Open Water Diver, 15 and over | 18 m (60 ft) | A certified buddy |
With the necessary training and experience, the limit of recreational diving is 40 m (130 ft). Going past 18 m (60 ft) is the job of the Advanced Open Water course.
Who can take the Open Water Diver course?
Anyone 10 or older who can swim, is medically fit and feels comfortable in the water. The course page lists three baseline criteria:
- Age: 10 or older. Divers aged 10 to 14 earn a Junior Open Water Diver certification, which becomes a regular Open Water Diver certification at 15.
- Water skills: swim 200 m (or yards) without stopping or aids, or 300 with mask, fins and snorkel, and float or tread water for 10 minutes.
- Health: a standard medical questionnaire. If it flags a condition, a doctor must sign off before you get in the water.
What theory does the Open Water course cover?
Five areas: your gear, pressure and your body, diving with a buddy, problems and emergencies, and dive planning. Octo splits them into 20 short lessons.
| Module | Lessons in Octo | What you learn | Go deeper |
|---|---|---|---|
| Your gear | 4 | Mask, fins, suit, BCD, regulator, alternate air source, gauges, buddy check | Glossary |
| Pressure and your body | 5 | Pressure and volume, equalizing, never holding your breath, buoyancy, air consumption | Boyle’s law, equalizing, buoyancy, air consumption |
| Diving with a buddy | 4 | Hand signals, descents and ascents, the safety stop, your air reserve, a lost buddy | Practice questions |
| Problems and emergencies | 4 | Running out of air, stress, decompression sickness, narcosis, cold and heat | Decompression sickness, narcosis |
| Planning your dives | 3 | Dive computers and no-decompression limits, the environment, planning, flying | Dive computers and NDL |
A handful of ideas carry most of the course:
- Pressure: in seawater, every 10 m (33 ft) adds 1 bar (1 atm). You’re under 2 bar (2 ata) absolute at 10 m (33 ft) and 3 bar (3 ata) at 20 m (66 ft).
- Volume: when the pressure doubles, a flexible air space halves. The biggest change happens between the surface and 10 m (33 ft).
- Breathing: never hold your breath on scuba, above all on the way up. Expanding air can tear your lungs.
- Air: reach the surface with at least 50 bar (500 psi), or the reserve set in the briefing.
- Safety stop: 3 minutes at 5 m (15 ft), on every dive.
- Lost buddy: search for no more than a minute, then ascend and meet at the surface.
- No-decompression limit: the time left at your depth before decompression stops would become mandatory. Your computer shows it; stay well inside it.
Worked example
Air at depth. A tank that would last you 60 minutes at the surface empties in proportion to the absolute pressure.
- At 10 m (33 ft), under 2 bar (2 ata): 60 ÷ 2 = about 30 minutes.
- At 20 m (66 ft), under 3 bar (3 ata): 60 ÷ 3 = about 20 minutes.
At 20 m (66 ft), the same tank at the same effort lasts a third of its surface time, so check your gauge more often as you go deeper.
Try a question from the app
breath-holding in a pool
In the deep end of the pool, a classmate takes a full breath from the regulator, takes it out and swims up holding their breath to talk to the instructor.
Show the answer
Answer C. The biggest volume changes happen near the surface. Lung injuries have occurred from pool depths.
How is the Open Water knowledge part assessed?
With questions along the way and a final exam at the end. The certification FAQ explains that you answer questions at the end of each chapter, then take a final exam that checks your knowledge of the basics. The Open Water Diver course page describes the study part as reading, videos and quizzes, about 5 to 10 hours of eLearning. You can also study with the manual.
Knowledge is one of three parts. You also practice skills in a pool or other calm, shallow water, then show them on four open water dives with your instructor.
Octo doesn’t contain the exam, the chapter questions or the manual: its own lessons and questions cover the same topics, to help you understand rather than memorize.
How should you study for the Open Water exam?
Little and often, with the numbers in your own units. A simple plan:
- Do your course reading first. Your instructor’s eLearning or manual is what the exam is built on.
- Learn the few numbers by heart: 18 m (60 ft), 50 bar (500 psi), 3 minutes at 5 m (15 ft), one minute to look for a lost buddy.
- Work the pressure math until it feels easy. Absolute pressure, volume and air use follow the same rule; the dive theory formulas sheet puts it on one page.
- Answer a few questions every day, and redo the ones you miss a day later, then a few days later. Spread your reviews out instead of cramming: see why you forget dive theory.
- Finish with a timed practice exam, then review the module where you scored lowest.
For a step-by-step version, read how to study for the Open Water exam. To test yourself now, try the Open Water practice questions, or the questions students most often get wrong.
Try a question from the app
safety stop
What is the recommended safety stop?
Show the answer
Answer D. 3 minutes at 5 m (15 ft), on every dive unless an emergency prevents it. It adds a margin against decompression sickness.
Frequently asked questions
How long does the Open Water Diver course take?
PADI’s course page puts the eLearning at 5 to 10 hours and the whole certification, with pool practice and four open water dives, at as little as 2 to 4 days. You can also study at home, then do the pool and open water dives on vacation with a dive center there.
Can a 10-year-old become an Open Water Diver?
Yes. With PADI, children can start at 10 and earn a Junior Open Water Diver certification. At 10 and 11, they stay above 12 m (40 ft) and dive with a dive professional or a certified parent or guardian. From 12 to 14, the limit is 18 m (60 ft), with a certified adult. The card becomes a regular Open Water Diver certification at 15.
Is the Open Water final exam hard?
It checks your knowledge of scuba diving basics, the same topics as the questions at the end of each chapter. If you understand pressure, buoyancy, air planning and the emergency procedures, and can say why each rule exists, you’re on solid ground. Take a timed practice exam first so the format feels familiar on the day, and see how to study for it.
What should you do after a long break from diving?
Refresh your skills in a pool or with a dive professional before your next open water dive: skills fade when you don’t use them, and so does the theory. Review the key numbers and procedures, check your gear, and plan an easy first dive in familiar conditions.
Can Octo replace my Open Water course materials?
No. Octo is an iPhone app to review theory: short lessons, explained quizzes, spaced review and a practice exam per level. It doesn’t replace your course materials, your instructor or your training in the water, and it doesn’t contain the official exam.
