How to study for the Open Water Diver exam
In short
To study for the Open Water exam, start about two weeks before your course: one or two short lessons a day, a quiz answered from memory, then spaced reviews of every question you miss. Master pressure, breathing, equalizing, air and emergencies. Testing yourself beats rereading. The night before, review your mistakes only, then sleep.
It’s 10 p.m. the night before your knowledge check. You’ve read the pressure chapter twice and it made sense both times, yet you can’t say what the absolute pressure is at 20 m (66 ft) without peeking. Rereading made the page familiar without training you to pull the answer from memory. This plan trains that recall in 10 to 15 minutes a day, starting two weeks out.
How is knowledge checked in the Open Water course?
Knowledge is usually checked twice: short quizzes as you study, then a final exam before you’re certified. For the PADI Open Water Diver course, PADI’s public FAQ says you answer questions at the end of each chapter and take a final exam at the end of the course. Its course page puts the eLearning at 5 to 10 hours, and its blog adds that most people spread this part over a few weeks and that your instructor reviews the material with you.
SSI’s published standards also require academic sections, assessments and a final exam. NAUI, CMAS and other agencies run similar but not identical courses, so ask your instructor how yours checks theory. Octo is an unofficial app, not affiliated with PADI: its questions are written for the app, not taken from any exam.
What should you master before the exam?
Master each safety rule and the reason behind it. Once you can explain why, a reworded question won’t throw you.
| Topic | You should be able to… | Read more |
|---|---|---|
| Gear | Say what each part of your scuba unit does; spot a valve that isn’t fully open | Open Water theory |
| Pressure | Show that absolute pressure doubles at 10 m (33 ft) and triples at 20 m (66 ft) | Boyle’s law |
| Your body | Equalize early and gently; explain why you never hold your breath | Equalizing |
| Air | Explain why your tank empties three times as fast at 20 m (66 ft); surface with 50 bar (500 psi) or the briefed reserve | Air consumption |
| Buddy | Read the main signals; search for a lost buddy for up to a minute, then meet at the surface | Practice questions |
| Emergencies | Rank your out-of-air options; recognize decompression sickness | Decompression sickness |
| Planning | Read your no-decompression limit; make a 3-minute safety stop at 5 m (15 ft) | Dive computers |
Try a question from the app
volume and pressure
A flexible bag holds 6 liters of air at the surface. You take it down to 20 m. What volume does it hold there?
Show the answer
Answer C. at 20 m the pressure is 3 bar, three times the surface, so the volume is a third: 6 ÷ 3 = 2 liters. Halving it would be right only at 10 m.
How do you study before the course?
Start about two weeks before your first session, with 10 to 15 minutes a day.
- Follow your instructor’s plan first. The agency’s eLearning or manual is the official route; Octo comes on top.
- Learn one or two lessons a day. Octo’s 20 Open Water lessons take 3 to 5 minutes each.
- Quiz yourself right away, from memory. Answer the six questions without looking back, then read every explanation.
- Do your review every day. In Octo, a missed question comes back the same day, then at longer and longer intervals.
- Say the “why” out loud for each mistake, in one sentence.
- Take a practice exam halfway and at the end. Octo’s has 30 questions, including real-life scenarios, and points to the module to review first.
Why do quizzes and spaced reviews work?
Pulling an answer out of memory strengthens it; rereading mostly makes the page feel familiar. In a classic experiment, rereading won on a test five minutes later, but students who had tested themselves remembered substantially more after two days and after a week (Roediger and Karpicke, 2006). A 2013 review of ten study techniques rated practice testing and spaced study as the most useful, and rereading and highlighting as low utility (Dunlosky and colleagues).
Timing matters too. In a study of more than 1,350 people, for a test a week after the review, the best gap before that review was about 20 to 40% of the week: one and a half to three days (Cepeda and colleagues, 2008). More in why you forget dive theory.
How do you study during the course?
Tie theory to what you just did in the water. After a pool session, redo the quiz of the matching lesson, such as equalizing or sharing air, and bring the questions you still miss to your instructor, whose word comes first. Between sessions, the Open Water practice questions give you one quick question per lesson, and the questions new divers get wrong show the traps to watch for.
Try a question from the app
why breath-holding is dangerous
What is the main danger of holding your breath while ascending on scuba?
Show the answer
Answer B. Lungs full of compressed air can’t hold the extra volume as the pressure drops: the tissue can tear. This lung overexpansion injury can kill.
What should you do the night before the Open Water exam?
The night before, review only what you got wrong, then sleep.
- Take your last practice exam earlier in the day, not at midnight.
- In the evening, redo your missed questions only. No new material.
- Say the key rules out loud: never hold your breath, equalize early, ascend slowly, watch your air, stay with your buddy.
- Sleep. Over a century of research shows that sleep helps you retain what you learned (Rasch and Born, 2013).
- On the day, read every option before you answer.
Frequently asked questions
How long does it take to study for the Open Water exam?
According to PADI, its Open Water eLearning takes 5 to 10 hours, and most people spread the knowledge part over a few weeks. On top of your course work, two weeks of 10 to 15 minutes a day with Octo, plus a review after each pool session, is realistic.
Is the Open Water exam hard?
It checks that you have a thorough grasp of scuba basics: gear, pressure and your body, buddy procedures, emergencies and planning. It feels hardest to students who only reread; quizzes from memory and spaced reviews are what research supports best.
Does Octo have the real Open Water exam questions?
No. Octo is an unofficial app, not affiliated with PADI or any other agency. Its 372 questions are written for the app, each with an explanation; they are not the real exam, the Knowledge Reviews or their answers. Your course materials come first.
Do I need to learn dive tables for Open Water?
Ask your instructor whether your course uses a dive computer, a table or both. Octo contains no tables: it teaches decompression through the dive computer and general principles. Either way, know what a no-decompression limit is and why it shrinks as you go deeper.
What calculations should I know for Open Water?
Octo’s Open Water lessons use three: absolute pressure (1 bar more every 10 m, or 1 atm every 33 ft, of seawater), volume (an air space halves when pressure doubles) and air use (a tank lasting 60 minutes at the surface lasts about 20 at 20 m, or 66 ft). See the formulas cheat sheet.
Sources
- Become a Certified Scuba Diver FAQs, official help center (read November 11, 2026)
- Open Water Diver, official course page and course FAQ (read November 11, 2026)
- Scuba Certification: Everything You Need To Know, official blog (updated July 12, 2026)
- SSI Training Standards, Open Water Diver (ISO 24801-2)
- Roediger and Karpicke, Test-enhanced learning, Psychological Science 17(3), 2006
- Dunlosky et al., Improving students’ learning with effective learning techniques, Psychological Science in the Public Interest 14(1), 2013
- Cepeda et al., Spacing effects in learning, Psychological Science 19(11), 2008
- Rasch and Born, About sleep’s role in memory, Physiological Reviews 93(2), 2013
