"1800s" vs. "1900s"

While for me the "1800s" refers to the whole period from "1800-1899", the "1900s" refers only to the period from "1900-1909".

I consider "the 1900s" as referring to 1900-1999.

It depends entirely on context, but with no context, I think I agree with the first post... if I mean 1900-1999, I would prefer "the 20th century".