I think of micros as being about the size of a 35mm film container, and nanos as the sort of size that screw-up name holders for dog collars are.

I've got a plastic container that I'll be using soon, and it's between the two. I'm not sure how to describe it, and I'd be interested to hear people's opinions.

It's a cylindrical plastic container with a screw top, and measures about 1.8 inches (4.5 cm) tall and 0.7 inches (1.8 cm) in diameter.