Since preferences for watch sizes change over the years, part of what makes a specific watch design timeless is a case diameter that is never going to be out of style. One of the hallmarks of an iconic and timeless watch design is a case diameter that has remained largely unchanged over the decades through which it has endured.
At 40mm in diameter, the Rolex Submariner achieves a perfect balance of possessing enough wrist presence, while still maintaining the ability to fly under the radar when necessary. Additionally, 40mm is large enough to look substantial on a wrist. It is not so massive that it places itself outside an acceptable range for most women.
Although Rolex redesigned the case of the Submariner several years ago to coincide with the addition of their Cerachom (ceramic) bezel insert. The brand did not change its 40mm diameter.
Given that Rolex designed a watch that would be viewed through a dive mask while exploring the oceans depths, the Submariner required a dial large enough that it could easily be referenced while in use underwater. Additionally, its case needed to be big enough to fit a rotating timing bezel, and robust enough to hold up to the rigors of scuba diving.
Upon its release, the Submariner was quite a large watch - especially considering the average size of wristwatches at the time. However, Rolex felt that their latest tool watch needed to be somewhat large in order to be useful and practical while performing its duties under the conditions for which it was intended.
Rolex has stayed true to their initial instincts, and for well over half a century, the Submariner watch diameter has been held at a relatively conservative 40mm. Many other watch manufacturers have significantly increased the overall sizes of their timepieces over the years, and while this does allow their designs to be in line with modern trends, it may inadvertently make them seem dated should smaller, thinner watches come back in style.
At 40mm in diameter, the Rolex Submariner hits a perfect size range that can be worn by almost any individual. Regardless of build or gender, the Rolex Submariner almost always looks at home on its owner.