Out of random interest, I wondered how thick a human hair is.
(What brought it to mind was reading about people flossing their teeth with their own hair, and wondering how wide a hair is. Plus recently reading about how proud Google are about their natural language processing and trying to give you what you want rather than what you asked for.)
The first page I found was this one, which collected a few other sources.
One of those made me weep.[*]
http://www.av.qnet.com/~dennyr/ apparently (the URL is 404 now) said: "Diameter of a human hair: inches: 0.001; centimeters: 0.00254".
Really? 0.00254 cm?
That would imply 0.00100 inches, not just 0.001.
It's like saying "Oh, he lives at least twenty miles [32.187 km] away!". Or even, "Of the seven participants, two (28.57%) tested positive for the dreaded lurgy."
Unwarranted precision makes me cry. ([*] Well, figuratively, at least.)
(Oh, and the answer to my question? Is apparently "it depends". Though 10–100 µm is apparently the basic order of magnitude.)
Oh dear, I just looked at the second hit I had opened in a tab. It contains this gem:
"Most is around 0.004 inches.
This equates to 0.00033333333333333333333333333333333333
Ow, it burns, it burns!