That's not quite correct. It's about the number of transistors per integrated circuit that minimises per-transistor cost. From the actual 1965 paper:
> "The complexity for minimum component costs has increased at a rate of roughly a factor of two per year (see graph on next page). Certainly over the short term this rate can be expected to continue, if not to increase. Over the longer term, the rate of increase is a bit more uncertain, although there is no reason to believe it will not remain nearly constant for at least 10 years. That means by 1975, the number of components per integrated circuit for minimum cost will be 65,000."
There's also the 1975 speech where he revised it down from a yearly doubling to once every two years.
