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There is no universal winner: the 42 mm fourth-generation Omega Planet Ocean 600M is rated to 600 metres, while the 41 mm heritage Seamaster 300 is rated to 300 metres. Both compared watches use calibre 8912 and offer a 60-hour power reserve. Choose based on whether you value the Planet Ocean’s higher depth rating or the Seamaster 300’s heritage design and slightly smaller stated diameter—then try both on and compare exact local prices.
Here, “Seamaster 300” means the heritage model, specifically reference 234.30.41.21.01.001. It is not the Seamaster Diver 300M, a separate Omega line.
How the specifications compare
This comparison pairs the Seamaster 300 reference 234.30.41.21.01.001, listed by OMEGA Japan, with the fourth-generation 42 mm stainless-steel Planet Ocean 600M introduced by Swatch Group in 2025. The figures below are for those cited models, not every configuration in either family.
| Specification | Seamaster 300 | Planet Ocean 600M |
|---|---|---|
| Case diameter | 41 mm | 42 mm |
| Thickness | 13.85 mm | 13.79 mm |
| Water resistance | 300 m / 1,000 ft | 600 m / 2,000 ft |
| Movement | Omega calibre 8912, automatic | Omega Co-Axial Master Chronometer calibre 8912, automatic |
| Power reserve | 60 hours | 60 hours |
Sources: OMEGA Japan’s Seamaster 300 product page and Swatch Group’s 2025 fourth-generation Planet Ocean release.
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The Planet Ocean has twice the stated water-resistance rating: 600 metres against the Seamaster 300’s 300 metres. That is a clear technical distinction, but it does not make the Planet Ocean the better everyday watch for everyone. Unless your diving needs call for the added rating, depth capability alone may not be a deciding benefit.
Fit is more than case diameter
The Seamaster 300 is 41 mm across and has a stated 48 mm lug-to-lug measurement. The Planet Ocean is 42 mm across. Their published thicknesses are nearly identical—13.85 mm and 13.79 mm respectively—so it would be misleading to call the Seamaster simply “thinner.”
Rank #2
- Blue Dial with Arabic Numeral and Index Hour Markers, Minute Track, Date Window, Luminescent Hands and Hour Markers
- Stainless Steel Case and Bracelet, Case Diameter: 43.5mm
- Anti-Magnetic, Resistant to Magnetic Fields Reaching 15,000 Gauss
- Self-winding Automatic Chronometer Movement, COSC Chronometer Certified and Co-Axial Escapement
- Scratch Resistant Sapphire Crystal with Anti-reflective Treatment, Exhibition Case Back
Diameter and thickness do not settle how either watch will sit on your wrist. Lug-to-lug length, case shape, bracelet articulation, weight, and wrist size also affect fit. The available specifications do not provide a directly comparable lug-to-lug figure for the new Planet Ocean, so they cannot establish which one wears smaller. Try both on if possible.
Movement and certification
For these two cited references, the movement is not a reason to choose one over the other: both use calibre 8912 and are listed with a 60-hour power reserve. The Planet Ocean release describes its movement as a Co-Axial Master Chronometer calibre 8912.
Rank #3
- Omega Seamaster Planet Ocean Automatic Men's Watch 215.33.44.22.01.001
OMEGA explains that Master Chronometer qualification includes COSC movement testing followed by METAS testing, and gives a precision range of 0 to +5 seconds per day. That is the brand’s explanation of the certification standard, not a comparative test of these two individual watches.
Heritage character or modern professional dive-watch style?
The Seamaster 300 is Omega’s heritage-oriented model. The Planet Ocean belongs to the brand’s modern professional dive-watch family, while drawing on earlier Seamaster design history. Swatch Group says the Planet Ocean launched in 2005 and “echoed the inspiration of the Seamaster 300 models from the 1960s.” That is a design lineage, not a claim that the two modern watches are interchangeable.
Rank #4
- Omega Seamaster Planet Ocean Automatic Men's Watch 215.30.44.21.01.002
Which one should you buy?
Choose the Seamaster 300 if
- You prefer its heritage design language.
- You want the smaller stated diameter of these two models.
- A 300 m rating is sufficient for your intended use.
Choose the Planet Ocean if
- You want the higher stated water-resistance rating of 600 m.
- You prefer the modern professional dive-watch approach.
- The specific 42 mm watch feels better on your wrist after trying it on.
Compare the exact local prices
OMEGA Japan’s catalogue listed selected new 42 mm steel Planet Ocean 600M configurations at ¥1,309,000 on a bracelet and ¥1,221,000 on rubber when accessed in 2026. These are Japan-specific snapshot prices, not a universal price comparison. The available sources do not provide a matched current price for Seamaster 300 reference 234.30.41.21.01.001. Check current prices in your region and compare the exact reference and bracelet or strap configuration before deciding.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
