36mm is the Datejust as Hans Wilsdorf intended it — the size that launched in 1945 and remained the standard for over 60 years. The 36mm Datejust is the historically correct proportion: large enough to read at a glance, refined enough to slide under any cuff. For wrists 6"–7.5", the 36mm is the collector's choice and the most versatile dress-sport watch in the Rolex catalog.
The current-production Datejust 36 uses the Cal. 3235 with 70-hour power reserve — the same movement as the 41mm. The 36mm is not a "smaller" watch — it's the original.