16 Divemaster dive theory practice questions
In short
16 practice questions for the Divemaster level, one per lesson of the Octo app, each with its answer and explanation. Tap an answer to check yourself. These are original questions written for the app, not taken from any agency’s exam; the app has six per lesson, spaced review and a 30-question practice exam.
The divemaster questions that catch people usually hinge on a small trap: gauge pressure where the gas laws need absolute, Celsius where they need kelvin, a MOD rounded up instead of down. Answer these 16 questions, one per lesson, on paper first, then open the explanation. Units are shown in metric with imperial in brackets. The theory behind them is on the Divemaster course page.
The 16 questions, lesson by lesson
Pressure and Boyle’s law
absolute pressure
1What is the absolute pressure at 25 m in seawater?
Show the answer
Answer B. 25 m of seawater adds 2.5 bar and the atmosphere 1 bar: 3.5 bar absolute. 2.5 bar is the gauge pressure, which is why “3.5 bar gauge” is wrong too; 3.4 bar uses the freshwater figure.
Temperature and gases: Charles’s law
absolute temperature
2Which value do you use for 25 °C in a gas-law calculation?
Show the answer
Answer C. Kelvin = °C + 273: 25 + 273 = 298 K. 485 mixes in the Fahrenheit constant (460); 25 K uses everyday degrees; 248 K subtracts instead of adding.
Partial pressures: Dalton’s law
ppO2 of air at depth
3What is the ppO2 of air at 40 m?
Show the answer
Answer B. 40 m is 5 bar absolute: 0.21 × 5 = 1.05 bar. 0.84 bar uses the gauge pressure; 3.95 bar is the ppN2. The percentage stays at 21%, but the partial pressure rises.
Gases in liquids: Henry’s law
Henry’s law
4Which statement is Henry’s law?
Show the answer
Answer C. Henry’s law links dissolved gas to partial pressure. A is Dalton’s law and B is Boyle’s law; a falling partial pressure makes gas leave the liquid, not dissolve.
Buoyancy calculations: Archimedes
apparent weight
5An object weighs 30 kg and displaces 20 L. What’s its apparent weight in seawater?
Show the answer
Answer A. The water displaced weighs 20 × 1.03 = 20.6 kg, so 30 − 20.6 = 9.4 kg. 10 kg uses fresh water; 20.6 kg is the lift itself; 50.6 kg adds instead of subtracting.
Breathing, circulation and carbon dioxide
the urge to breathe
6What normally triggers your urge to breathe?
Show the answer
Answer B. CO2 is the main trigger. Low oxygen plays only a weak backup role, which is why it can go unnoticed until a blackout.
Decompression theory
half-time arithmetic
7A 20-minute compartment starts in balance with the surface. After 40 minutes at a constant depth, how close is it to saturation?
Show the answer
Answer B. Two half-times: 50% after the first, then half of the remaining 50%, so 75%. 100% assumes a steady, linear fill; 87.5% takes three half-times.
Toxic and narcotic gases
CNS oxygen toxicity
8Why is CNS oxygen toxicity so dangerous underwater?
Show the answer
Answer B. Warning signs don’t always appear. A convulsion underwater can cost the diver their regulator and their airway. Hence the MOD and gas analysis.
Regulators, cylinders and dive computers
balanced first stage
9What does a balanced first stage offer?
Show the answer
Answer A. Balancing removes the effect of cylinder pressure on the valve. Protection against freezing comes from environmental sealing, and every regulator needs servicing.
The divemaster’s role
what a divemaster does
10Which task is part of a divemaster’s role?
Show the answer
Answer B. A divemaster supervises certified divers, assists instructors and handles logistics. Teaching and certifying belong to instructors; medical statements belong to physicians.
Giving a dive briefing
purpose of a briefing
11Apart from sharing the plan, what does a briefing give you?
Show the answer
Answer A. During the briefing, you see who listens, who looks nervous and who seems unsure of their gear. It doesn’t transfer responsibility or replace the buddy check.
Supervising certified divers
roll call after the dive
12When do you take the roll call after a dive?
Show the answer
Answer A. The count must match before the boat moves or anyone leaves the site, after every dive. A missing diver is easiest to find right away and on the spot.
Assisting with training
who leads a course
13During a course, who is responsible for teaching and evaluating skills?
Show the answer
Answer A. The instructor teaches, evaluates and certifies. You assist as directed, within your agency’s standards.
Mapping a dive site
why map a site
14What is the main use of a site map for a divemaster?
Show the answer
Answer A. A map shows the layout, depths, hazards and entry points in seconds, which makes briefings clearer and routes easier to follow.
Managing risk
hazard and risk
15What’s the difference between a hazard and a risk?
Show the answer
Answer A. A hazard is a source of harm; risk combines the likelihood of harm and its severity. That’s what you reduce by avoiding, reducing or preparing.
Professional skills and career
customer service
16A nervous guest is on their first boat dive. Which response shows good service?
Show the answer
Answer A. Attention and clear information calm nerves, and a thoughtful buddy pairing adds support. A diver who feels looked after dives more safely.
Frequently asked questions
Are these the real Divemaster exam questions?
No. These are original practice questions written for the Octo app. They cover the theory of the Divemaster level, but they are not taken from any training agency’s exams, knowledge reviews or manuals, and Octo is not affiliated with PADI or any other agency.
How many Divemaster questions does Octo have?
Octo has six questions for each of its 16 Divemaster lessons, 96 in all, each with the right answer and an explanation, plus a 30-question practice exam for the level that includes real-life scenarios, with an optional timer. See how Octo works.
What should I do with the questions I get wrong?
Reread the explanation, say in one sentence why the right answer is right, then try the question again a day or two later. In Octo, spaced review does this for you: a missed question comes back the same day, then at longer and longer intervals until you know it. The divemaster theory study plan builds this into six weeks.
What math do the Divemaster questions use?
Arithmetic: multiply, divide, add or subtract 1. You need absolute pressure (depth ÷ 10 + 1 bar, or depth ÷ 33 + 1 ata), the gas laws, partial pressures and simple buoyancy. Every formula is worked in both unit systems on our dive theory formulas sheet, with the trap that catches people.
