Descent Mk3i Dive Computer 51mm

The Garmin Descent Mk3i 51mm is one of the most capable dive computers on the market — a full-featured air-integrated dive computer watch built for recreational, technical and freediving, with the multisport GPS chops to hold its own as an everyday smartwatch between dives. If you're looking for a single device that handles everything from trimix tec dives to trail runs to contactless payments, this is it. The headline feature is SubWave™ sonar-based communication — Garmin's proprietary underwater networking technology that lets you exchange preset diver-to-diver messages up to 30 metres away and monitor tank pressure and depth for up to 8 divers within a 10-metre range. Pair the Mk3i with Descent T2 transceivers  and you get fully wireless, hoseless air integration on up to 8 tanks . It's a genuinely impressive piece of engineering. The Dive Readiness Tool is another Garmin first — it analyses your sleep quality, stress levels, exercise load and jet lag to give you an honest assessment of whether your body is actually ready to dive that day. Factor in DiveView™ colour maps with bathymetric depth contours and 4,000+ dive sites, the Bühlmann ZHL-16c decompression algorithm with fully customisable gradient factors, and up to 66 hours of battery life in dive mode , and you've got a computer that's as serious about diving as you are. The 51mm case houses a bright 1.4" AMOLED display with scratch-resistant sapphire lens, leakproof inductive metal buttons and a 200-metre dive rating. It's a big watch — properly sized for glove-friendly use underwater — and the display is genuinely readable in all conditions, including a dedicated Lume Mode for night dives. Key Features SubWave™ sonar underwater communication — exchange preset diver-to-diver messages up to 30 m; monitor tank pressure and depth for up to 8 divers within 10 m range Wireless air integration — pairs with up to 8 Descent T2 transceivers (sold separately) via SubWave™ sonar; no hose required Multiple dive modes — single gas, multi-gas (nitrox & trimix), gauge, apnea, apnea hunt, pool apnea and closed-circuit rebreather (CCR) Bühlmann ZHL-16c decompression algorithm with gradient factors, customisable conservatism (low/medium/high or custom GFs), deep stops and missed deco lockout DiveView™ colour maps — bathymetric depth contours and 4,000+ dive sites preloaded; find new sites and get oriented before you even hit the water Dive Readiness Tool — Garmin-first technology that factors in sleep, stress, exercise and jet lag to help you decide when you're genuinely ready to dive NDL Aware™ depth metrics — real-time display showing how specific depth changes will impact your no-decompression limit, helping you extend bottom time safely Gas mixes — Air, Nitrox and Trimix up to 100% O₂; 1 bottom gas plus up to 11 deco and/or backup gases Up to 66 hours battery in dive mode (40 hours with air integration active) 1.4" AMOLED colour display , 454 x 454 px, with scratch-resistant sapphire lens — readable in all light conditions Built-in LED flashlight — variable intensities and strobe modes; works above and below water Lume Mode — ambient light sensor applies green luminescence to the watch face to aid readability and protect night vision on night dives Big Numbers Mode — simplified dive screen with larger text for critical data at a glance, great with gloves on 3-axis dive compass — adjustable heading, quick-change to 90R/90L and reciprocal; displays degrees and direction back to set heading Surface GPS with Reference Point — track entry and exit points on the surface and drop right onto your dive site every time Variometer — tone and vibration feedback on freedive descent and ascent rates Sidemount tank switch guidance — visual reminders to switch tanks at a preset pressure value when paired with a T2 transceiver, keeping buoyancy balanced and gas supply managed Post-dive activity guidance — alerts you when it's advisable to postpone training after a dive to reduce the risk of decompression sickness Customisable dive screens — build the data layout you want for each dive mode Dive log with Garmin Dive™ app sync — log dives, track gear, take notes; auto-uploads via the Garmin Dive smartphone app inReach® device compatible — pair with an inReach device and dive case for satellite messaging when you're well off-grid Tide data — current ocean conditions via paired smartphone Customisable alarms — audible and vibration alerts for ascent rate, PO₂, CNS/OTU, NDL, deco, gas switching, tank pressure and gas consumption rate; up to 40 per dive mode Multisport GPS — preloaded activity profiles for trail running, swimming, cycling, hiking, skiing, rowing, golf, surfing and more Surf metrics — waves surfed, max speed, distance; Surfline Sessions™ integration for video of every wave Health monitoring — wrist-based heart rate, Pulse Ox blood oxygen saturation, sleep tracking with Sleep Score, VO2 max, Training Status, Training Readiness, Endurance Score and Hill Score Breathing Variations — monitors shifts in breathing patterns during sleep that may indicate conditions such as sleep apnea Jet Lag Adviser — personalised guidance on light exposure, sleep schedule and exercise to minimise jet lag; particularly useful for liveaboard travel Garmin Coach — tailored training plans keyed to your goals and fitness data Multi-band GPS with SATIQ™ technology — superior positioning accuracy with optimised battery consumption Preloaded TopoActive maps (multicontinent) and SkiView™ maps for 2,000+ ski resorts worldwide PacePro™ technology — GPS-based pace guidance for race-day strategy Music storage — download from Spotify, Deezer, Amazon Music or YouTube Music for phone-free listening Garmin Pay™ contactless payments with participating providers Smart notifications — emails, texts and alerts via paired iPhone or Android smartphone Safety and incident detection — sends your live location to emergency contacts if an incident is detected Connect IQ™ Store — add watch faces, data fields and third-party apps QuickFit™ 26 mm band compatible — swap bands tool-free Leakproof inductive metal buttons — no exposed seals to degrade over time Technical Specifications Physical size 51 x 51 x 16.4 mm Display 1.4" (35.56 mm) AMOLED colour, 454 x 454 px Lens Sapphire crystal Bezel Diamond-like Carbon (DLC) coated titanium / PVD-coated titanium (variant dependent) Case Fibre-reinforced polymer with titanium rear cover Buttons Leakproof inductive metal Strap material Silicone (standard & extra long) / DLC coated titanium bracelet (variant dependent) QuickFit™ compatible Yes — 26 mm Wrist circumference Silicone band: 135–230 mm | Extra long silicone: 135–355 mm | Titanium bracelet: 135–220 mm Weight — no band 77.8 g Weight — silicone band 105.6 g Weight — titanium band 165.9 g Water rating Dive rated to 200 m Charging Garmin proprietary USB-C clip charger Memory 32 GB Decompression model Bühlmann ZHL-16c with gradient factors Dive modes Single gas, multi-gas, gauge, apnea, apnea hunt, pool apnea, CCR Gas mixes Air, Nitrox, Trimix — up to 100% O₂; 1 bottom gas + up to 11 deco/backup gases PO₂ limit Up to 2.0 (customisable deco PO₂) Air integration Yes — wireless via SubWave™ sonar; up to 8 Descent T2 transmitters Conservatism Low / medium / high or fully custom gradient factors Safety stop Customisable — off / 3 min / 5 min Deep stops Yes — via custom gradient factors Missed deco lockout Yes (can be disabled prior to dive with user acknowledgement) Dive planner Basic NDL + multi-gas deco planner Altitude adjustment Automatic Alarms Audible & vibration — ascent rate, PO₂, CNS/OTU, NDL, deco, gas switch, tank pressure, gas consumption rate; up to 40 customisable per dive mode Battery — Smartwatch mode Up to 25 days (10 days always-on display) Battery — Battery Saver Watch Up to 31 days Battery — GPS Only Up to 76 hours (56 hours always-on) Battery — All Satellite Systems Up to 55 hours (43 hours always-on) Battery — All Satellites + Multi-band Up to 48 hours (38 hours always-on) Battery — All Satellites + Music Up to 17 hours Battery — Max Battery GPS Up to 118 hours Battery — Expedition GPS Up to 24 days Battery — Dive Mode Up to 66 hours Battery — Dive Mode with Air Integration Up to 40 hours FAQ Is the Garmin Descent Mk3i 51mm good for technical diving? Yes — it's a fully capable tec dive computer. It supports trimix, nitrox (up to 100% O₂), CCR and multi-gas dives with 1 bottom gas plus up to 11 deco and backup gases. The Bühlmann ZHL-16c algorithm with fully customisable gradient factors, deep stops and missed deco lockout make it suitable for serious technical divers. It also calculates CNS and OTU oxygen toxicity tracking throughout the dive. Do I need to buy the T2 transmitter for air integration? Yes. The Descent T2 transceiver is sold separately (also available as a bundle with some models). The watch communicates with T2 transmitters wirelessly via SubWave™ sonar — so no hose, no wired connections. You can run up to 8 transmitters simultaneously, making it a strong choice for dive guides and dive leaders monitoring a group. What's the difference between the Garmin Descent Mk3i 43mm and 51mm? The 51mm has a larger 1.4" AMOLED display (vs 1.2" on the 43mm), longer battery life across most modes, and uses a 26 mm QuickFit band (vs 20 mm). The feature set is essentially identical — the choice comes down to wrist size and personal preference for display size. If you're between the two, most divers with medium to large wrists prefer the 51mm for on-wrist readability underwater. Can I use the Descent Mk3i 51mm for freediving? Absolutely. It has dedicated apnea, apnea hunt and pool apnea modes, a variometer that provides real-time tone and vibration feedback on descent and ascent rates, Pulse Ox blood oxygen monitoring, and a dive log that records all your sessions. It's a serious freediving computer as well as a scuba one. How does the Dive Readiness Tool work? The Dive Readiness Tool pulls together data the watch is already collecting — sleep quality and duration, stress levels (via HRV), recent exercise load, and any jet lag — and combines it into a single readiness score. It's not infallible, but it's a genuinely useful nudge for days when you're feeling off and can't quite put your finger on why. Think of it as a second opinion before you kit up. Is the Descent Mk3i 51mm good as an everyday smartwatch? Very much so. Up to 25 days in smartwatch mode, full GPS multisport tracking, onboard music (Spotify, Deezer, Amazon Music, YouTube Music), Garmin Pay contactless, smart notifications, and comprehensive health tracking including sleep, Pulse Ox and HRV. The AMOLED display is genuinely excellent for a dive computer. The only real-world caveat is that the 51mm is a large watch — wrist presence is significant. What's in the box? The Descent Mk3i 51mm comes in three versions: Carbon Grey DLC Titanium with Black Silicone Band — Descent Mk3i 51mm, black extra-long adjustment strap, USB-C clip charging/data cable, documentation (available as a bundle with T2 Transmitter) Carbon Grey DLC Titanium with DLC Titanium Band — Descent Mk3i 51mm, black QuickFit™ 26 silicone band, black extra-long adjustment strap, USB-C clip charging/data cable, documentation (available as a bundle with T2 Transmitter) Silver and Black PVD Titanium with Black/Pebble Grey Silicone Band — Descent Mk3i 51mm, black extra-long adjustment strap, USB-C clip charging/data cable, documentation ( T2 Transmitter available separately ) Read our dive computer care and maintenance guide to keep your Mk3i performing at its best. VIDEO CONSULTATIONS NOW AVAILABLE: We're bringing our highly experienced and knowledgeable staff to you with live-streaming consultations. 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