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This is a buying comparison, not dive training or dive-planning guidance. Scuba diving carries real risks, including decompression sickness. Follow your training agency’s guidance and each manufacturer’s own documentation, dive within your certification level, and never treat a wrist computer — built-in or app-based — as a substitute for a dive buddy, a backup computer, or proper training. Prices are approximate, current as of publication, and change frequently — confirm the latest price with the retailer before buying.Published August 9, 2026. Updated October 10, 2026.
Short version: Garmin Descent Mk3 and Suunto Ocean are dedicated dive computers, each EN13319-certified with a named, adjustable decompression algorithm built in and no subscription required. Apple Watch Ultra 3’s hardware carries the same EN13319 rating to 40 meters, on Apple’s own spec sheet — but reaching a working algorithm needs a separate Oceanic+ app subscription the watch’s price doesn’t include. Between the two dedicated computers, Suunto Ocean matches Garmin’s certification and comes within a shade of its gas planning for about $400 less, with a battery that runs twice as long in dive mode. Garmin’s case is rated to 200 meters against Suunto’s 60. That depth gap is the actual reason to pay more, not the certification itself.
I have scuba dived and snorkeled the reefs at John Pennekamp in the Florida Keys. Those are recreational dives, and they showed me what a wrist computer is for. You need a clear screen, a decompression number you can trust, and a battery that outlasts the trip. A deeper case rating does not matter on a reef. The certification and the algorithm do.
How do we score dive computers?
Certification and algorithm documentation carry the most combined weight here — 50 of 100 points — because those two things are what actually separate a dive computer from a watch with a depth gauge. Battery and dive-log documentation split 30 points, because they matter to a buyer without defining the category. Price takes the remaining 20.
What does each dive computer score?
| Axis (weight) | Garmin Descent Mk3 | Suunto Ocean | Apple Watch Ultra 3 |
|---|---|---|---|
| Certification documentation (25) | 25 — EN13319, built in, no subscription | 25 — EN13319, built in, no subscription | 15 — EN13319 hardware rating exists, but the algorithm that makes it usable sits behind a paid app |
| Algorithm & gas-mix documentation (25) | 25 — Bühlmann ZHL-16c, configurable Gradient Factors, air/nitrox/trimix/100% O2 | 24 — Suunto Bühlmann 16 GF, configurable, nitrox and multigas to 5 gases 21–100% O2 | 14 — Bühlmann ZHL-16C via Oceanic+, air or nitrox to 40% only, no trimix |
| Dive-mode battery, published (20) | 10 — up to 30 hrs (43mm, always-on) | 20 — up to 60 hrs, the longest published figure | 5 — no dive-specific figure published by Apple or Oceanic |
| Dive-log capacity, published (10) | 4 — capacity not published; logs sync to the Garmin Dive app | 4 — capacity not published; oldest dive overwritten when full | 4 — logs live in the Oceanic+ app; no count published |
| Cost to actually dive with it (20) | 13 — $1,199.99, nothing further to buy | 20 — $799, nothing further to buy | 18 — $799 hardware plus $79.99/yr minimum for the Oceanic+ tier that unlocks scuba planning |
| Tally | 77 | 93 | 56 |
What if you weight the axes differently?
Disagree with a weight? The math is right there. Move ten points from certification to price and Suunto’s lead barely moves — this isn’t a close call being dressed up as one.
None of the three turned up in a CPSC recall search or a Health Canada recall search run against the maker and product names above. Clean on both, as of publication.
How long does the Garmin Descent Mk3 battery last?
Up to 30 hours in dive mode, for the 43mm model. The Descent Mk3, 43mm, runs $1,199.99. That’s the base model — no air integration, no transceiver, no built-in flashlight. The case is rated to 200 meters, and the watch runs Garmin’s Bühlmann ZHL-16c algorithm with configurable Gradient Factors. Gas planning covers a bottom gas plus up to 11 backup or decompression mixes: air, nitrox, trimix, and 100% oxygen. Dive logs sync to the Garmin Dive app; Garmin’s spec table does not print an on-device dive count.
Here’s the part worth slowing down for. Garmin’s own Descent Mk3 press release headlines “up to 66 hours” of dive-mode battery — a real number, not invented, but footnoted to the larger 51mm Mk3i. The 43mm Mk3 priced and compared here is rated up to 30 hours in dive mode with the display always on, according to Garmin’s own owner’s manual. Not a rounding difference. Sixty-six hours reads like nearly three days of diving. Thirty is a bit over one.
Case size buys battery here, quietly, in the fine print rather than the headline.
Skip this if you don’t dive past recreational limits or need trimix planning named on the spec sheet. You’re paying for depth and gas range most divers never touch, and Suunto documents the certification that actually matters for $400 less.
Does the Suunto Ocean need a subscription?
No. The Ocean, the All Black model, currently lists at $799 on Suunto’s own site — down from its $899 launch price. EN13319-certified to 60 meters, comfortably past where recreational no-decompression diving happens. The algorithm is Suunto Bühlmann 16 GF, gradient factors configurable the same way Garmin’s are. Gas planning covers nitrox and air plus multigas support up to five gases between 21% and 100% oxygen; Suunto’s own copy stops short of printing the word “trimix,” though the gas range functionally covers most of what that word implies.
Battery is the standout number: up to 60 hours in dive mode, the longest published figure of the three, and up to 16 days in everyday smartwatch use with heart rate on. Independent test notes from DIVE Magazine’s review land in the same range. One real gap: Suunto’s support documentation says the logbook simply overwrites the oldest dive once memory fills, without stating how many dives that actually is. Garmin’s spec table does not print a dive count either.
Skip this if you’re diving past 60 meters or want “trimix” printed in the marketing copy rather than implied by the gas-mix range — the Mk3’s deeper case and explicit language are the two things Ocean doesn’t match.
Does Apple Watch Ultra 3 work as a dive computer?
Only with a paid app. Apple Watch Ultra 3 launched at $799, and Apple’s store now sells its successor, Ultra 4, from the same $799 — the cheapest hardware of the three. Apple’s own technical specifications page states the watch “meets EN13319 recreational scuba diving to 40m (±1m accuracy)” under its 100-meter water resistance rating (ISO 22810:2010). That’s a genuine, published certification claim, sourced directly from Apple’s own spec sheet, and it puts the watch’s hardware in the same regulatory category named by the two dedicated computers above.
What does the Oceanic+ subscription cost?
What that sentence doesn’t say up front: the watch doesn’t ship with a working decompression algorithm. Reaching one means installing Oceanic+, a third-party app from Oceanic Worldwide, and paying for its Scuba Diving tier — $9.99 a month, $79.99 a year, or $4.99 a day, per Oceanic’s own pricing page. The free tier bundled with the watch covers GPS tracking, a compass, and basic depth monitoring. It does not include dive planning or the Bühlmann ZHL-16C algorithm that makes the EN13319 rating something you can actually dive with. Once subscribed, Oceanic+ plans for air or nitrox up to 40% oxygen, with no trimix option, and neither Apple nor Oceanic publishes a dive-specific battery figure separate from the watch’s general rating of up to 42 hours, 72 in low power mode.
Skip this if you want a dive computer that works the day it arrives. The $799 sticker doesn’t include the subscription that turns the certification into something usable, and the two dedicated computers above don’t ask for one.
Do dive computers match their marketing claims?
Four claims, checked against each maker’s own documentation — not a review, a forum thread, or a retailer listing.
| Claim | Source | What the documentation actually shows | Verdict |
|---|---|---|---|
| “Up to 66 hours” in dive mode | Garmin’s Descent Mk3 press release | Footnoted to the 51mm Mk3i. The 43mm Mk3 compared here — the model actually priced at $1,199.99 — is rated up to 30 hours in dive mode with always-on display, per Garmin’s own owner’s manual | Accurate, for a different case size |
| “Meets EN13319 recreational scuba diving to 40m” | Apple’s own Apple Watch Ultra 3 tech specs page | True for the watch hardware. Using it requires installing Oceanic+ and paying for its Scuba Diving tier — not mentioned on the spec sheet itself | Accurate, incomplete without the subscription cost |
| “EN13319 certified to 60m” | Suunto’s own Ocean product and support pages | Matches Suunto’s documentation with no discrepancy found | Accurate as stated |
| Supports trimix diving | Garmin’s published Descent Mk3 gas-planning specs | Confirmed: bottom gas plus up to 11 deco/backup gases including trimix and 100% oxygen | Accurate as stated |
What are the dive computers’ specs side by side?
| Garmin Descent Mk3 (43mm) | Suunto Ocean (All Black) | Apple Watch Ultra 3 | |
|---|---|---|---|
| Price | $1,199.99 | $799 (was $899) | $799 (hardware only) |
| Case dive rating | 200 m | 60 m | 100 m water resistance |
| Dive-computer certification | EN13319 | EN13319 | EN13319 to 40m — hardware only, needs a third-party app |
| Decompression algorithm | Bühlmann ZHL-16c, configurable GF | Suunto Bühlmann 16 GF, configurable | Bühlmann ZHL-16C, via Oceanic+ app |
| Gas mixtures | Air, nitrox, trimix, 100% O2 (up to 11 backup/deco gases) | Air, nitrox, multigas to 5 gases, 21–100% O2 | Air or nitrox to 40% (Oceanic+ Scuba tier) |
| Dive-mode battery | Up to 30 hrs (always-on) | Up to 60 hrs | Not separately published |
| Smartwatch-mode battery | Up to 10 days | Up to 16 days (HR on) | Up to 42 hrs (72 hrs low power) |
| Dive-log capacity | Not published; syncs to Garmin Dive app | Not published | Stored in-app; not published |
| Ongoing cost to dive | None | None | $79.99/yr minimum (Oceanic+ Scuba tier) |
Prices are approximate, current as of publication, and change frequently — confirm the latest price with the retailer before buying.
Which dive computers should you buy?
The Ledger isn’t close between the two real dive computers here — 93 to 77 sounds decisive until you look at where the 16 points actually come from. Dive-mode battery and price, not certification or algorithm depth, which are functionally tied.
If I were spending my own money and didn’t need a 200-meter case or a marketing page that spells out “trimix,” I’d buy the Suunto Ocean. Same certification. A comparable algorithm. Twice the dive-mode battery. Four hundred dollars still in my pocket. Descent Mk3 earns its price if you actually dive past recreational limits on a regular basis. Most people reading a comparison like this one don’t, and know it.
Where do the three dive computers finish?
Suunto Ocean wins this Ledger. Garmin Descent Mk3 loses on value, not on capability — it’s the more capable watch on paper, priced like it, and that’s a defensible trade for the diver who needs the depth.
Apple Watch Ultra 3 loses outright as a dive computer. Real EN13319 hardware, sold without the software that makes the rating mean anything, at a price that looks like the best deal of the three until the subscription bill arrives. None of that makes Ultra 3 a bad watch. It just isn’t a dive computer out of the box, and the spec sheet that names the certification doesn’t say so.
Comparing Ultra 3 against watches built for the same everyday-adventure category instead of diving specifically? See our adventure smartwatch comparison. GPS battery claims get the same claims-check treatment in our GPS running watch battery breakdown. Browse more in our Wearable Tech category.
