Scuba certification levels, agency by agency.

The common shape

Under the ISO 24801 framework, a diver moves from supervised diving (Level 1) to autonomous diving (Level 2) and then to dive leader (Level 3). Most agency ladders follow that outline and add an advanced course, rescue training and instructor levels. Ages and prerequisites below are each agency's own published statement for the named course, with the page date where the agency gives one; where the page carries no date we say it is undated (we read those pages in October 2026). Depth figures are gathered on depth limits by certification.

PADI

PADI's blog (Sarah Wormald, updated 31 August 2024) lays out the ladder as Open Water Diver, Advanced Open Water Diver, Rescue Diver, Divemaster, then Open Water Scuba Instructor. Before Open Water Diver there is a shorter option, Scuba Diver, which PADI's 2018 blog calls a subset of Open Water Diver for diving under the direct supervision of a PADI Professional.

PADI calls Divemaster its first professional level.

SSI

SSI's entry steps are Scuba Diver, which SSI says is for diving with an SSI Professional, and Open Water Diver. Its Advanced Adventurer, in an archived SSI standard, requires Junior Open Water or Open Water Diver and at least five different Adventure Dives. SSI's advanced training pages describe Specialty Diver, Advanced Specialty Diver and Master Diver as recognition ratings that a diver earns automatically after a set number of specialities, rather than separate courses. SSI describes Divemaster as the first professional step; Divemaster or an equivalent is needed to enter its Instructor Training Course, which leads to an Instructor Evaluation for Open Water Instructor.

NAUI

NAUI's supervised entry course is Scuba Diver (Supervised Diver, ISO Level 1). According to NAUI's undated course pages, its Rescue Scuba Diver requires NAUI Open Water Scuba Diver or an equivalent plus current CPR, first aid and emergency oxygen certifications, with a minimum age of 15 by the water phase and junior certification for ages 10 to 14. NAUI says Rescue Scuba Diver is the required rescue training for its Skin Diving Instructor, Assistant Instructor, Divemaster and Instructor ratings. NAUI Master Scuba Diver requires Advanced Open Water Scuba Diver and Rescue Scuba Diver or equivalents and a minimum age of 15 by the water phase; NAUI presents it as a step towards leadership ratings. We did not find a current NAUI primary page for its autonomous open water course, its advanced course or its Divemaster prerequisites, so those are not described here.

BSAC

BSAC's ladder is Ocean Diver, Advanced Ocean Diver, Sports Diver and Dive Leader. BSAC's milestones page says it introduced new diver grades in 1984: Novice (now Ocean Diver), Sports, Dive Leader and Advanced Diver. BSAC says Sports Diver adds deeper dives with decompression stops and rescue skills. Its equivalency page maps Ocean Diver to the Open Water and Advanced Open Water level grades of other agencies, Sports Diver to Rescue Diver level grades and Dive Leader to Divemaster level grades.

CMAS

CMAS uses stars. Wikipedia (secondary) describes One Star as competent in sheltered open water, Two Star as having some open water experience and Three Star as competent to supervise other divers. BSAC's equivalency page lines CMAS One Star up with its Ocean Diver, Two Star with Sports Diver and Three Star with Dive Leader, with Oxygen Administration also required at that level.

SDI

SDI's undated course pages give these figures. Its Junior Open Water Scuba Diver starts at age 10 with parental consent; juniors aged 10 to 14 train and dive under the direct supervision of a parent, guardian or active dive professional and may upgrade to Open Water Scuba Diver at 15. SDI describes Open Water Scuba Diver in three parts: eLearning, pool training and supervised open water dives. Advanced Adventure Diver covers five specialities, two of them required (Deep and Navigation), and SDI says completing it qualifies a diver to enrol in SDI Rescue Diver. SDI's minimum age for it is 18, or 10 with parental consent.

GUE

GUE's recreational path runs from Discover Diving, a trial, to Supervised Diver or Open Water Diver (formerly Recreational Diver Level 1), then Recreational Diver 2 (now Advanced Open Water Diver) and Recreational Diver 3. A separate course, GUE Fundamentals, has a minimum age of 16 on GUE's undated course page and requires an autonomous entry-level card from a recognised agency. GUE says it is the prerequisite for all GUE courses except the entry-level courses and its Drysuit and Doubles primers. It ends in either a recreational pass, which opens advanced recreational classes, or a technical endorsement, which leads to GUE's technical and cave curricula.

RAID

RAID's "Start Diving" menu lists Try Dive, Indoor Diver, Open Water, Explorer 30, Advanced 35 and Scuba Diver. We did not find RAID pages giving the ages and limits for Explorer 30 and Advanced 35.

Moving between agencies

Many of the course pages above accept another agency's card as a prerequisite, with wording such as "or equivalent" (NAUI, SDI), "or a qualifying certification" (PADI) or "an autonomous entry-level certification from a recognised agency" (GUE). The pages we read do not list which cards qualify. BSAC's equivalency page adds that grades it treats as equivalent may not carry the same autonomous depth qualification.