Quote fromOne block is a cubic meter, or 1x1x1 m. The avatar is 1.7 m and fits in a two block space. Default creative maps are 128^3, 256^3, and 512^3, with sea level being in the center. 64 below, 64 above for the small one, 128 and 128 for the medium sized one, and 256 and 256 for the large one. Custom servers have even larger maps, though. I've seen maps as large as 4096x256x4096 (Islands of Kyth, for you older people who might still faintly remember it).
Much more detailed than my description.
I'm interested, how did you find the height of the man?