Do we all really have 90,000 to 150,000 hairs?

[DreamSheep]

Sometimes I get bored and get a bit geeky, and am questioning if it is true that we all have 90,000 (redheads) to 150,000 hairs (blonde hair) on our heads.
Because the overall hair thickness seems to vary from ~1 inch all the way up to 5inch, and because the cross section of the ponytail ideally should be circular, and perimeter increases of one inch means that there is an ever greater increase in area, meaning that someone with a 2 inch ponytail has over twice the amount of hair as someone with a one inch ponytail, and the same applies to a 4 inch ponytail.

So when doing these calculations, but with specific hair widths (which is 50micrometers for very fine fair, 150micrometers for thick, coarse hair), and super thick ponytails with fine hair seem like they should have well over 200,000 hairs, on occasions even 300,000 (although there will be air spaces in between) - so does anyone else think this data is a bit off?

I can show graphs if anyone wants them, my geekiness and random hair thoughts HAS lead me to plot this out in Excel.

[Lindenare]

I don't know how the estimates for number of hairs by hair color were arrived at, but I think that measuring number of hairs by ponytail volume has too many variables for accuracy. A better method would be to count the hairs in a square inch, then estimate the area of the scalp. Assuming that most people's hair density is relatively constant, the estimate arrived at should be fairly accurate.

Also, 90,000 and 150,000 aren't upper limits - they are averages. It stands to reason that some people would have many more hairs, but they would be the outliers in their categories. (Just out of curiosity, what were the units used for the 50 and 150 values for hair widths?)

[DreamSheep]

I don't know how the estimates for number of hairs by hair color were arrived at, but I think that measuring number of hairs by ponytail volume has too many variables for accuracy. A better method would be to count the hairs in a square inch, then estimate the area of the scalp. Assuming that most people's hair density is relatively constant, the estimate arrived at should be fairly accurate.

Also, 90,000 and 150,000 aren't upper limits - they are averages. It stands to reason that some people would have many more hairs, but they would be the outliers in their categories. (Just out of curiosity, what were the units used for the 50 and 150 values for hair widths?)
Hmm, I don't know, I would prefer the pony method because it gathers all longish hair, whereas I wouldn't be surprised if hair density varied from crown o other scalp regions. Hmm, and I suppose if they are averages, it would be nice to know what sort of range they lie in.

The units are miicrometers - have edited post to include that, my bad!

[StellaKatherine]

each hair strand is different thickness as well. There can be 2 people having identical amount of hairs all over the head. One has fine hair and other coarse hair. The Coarse hair owner will have probably double size ponytail that the fine hair person...

[chen bao jun]

I have no intention of trying to count even one square inch.

[Beborani]

I need to know these numbers for other reasons than just curiosity and here is an old paper that maybe helpful.
http://journal.scconline.org/pdf/cc1977/cc028n05/p00219-p00230.pdf

Ponytail measurement is layperson's method and is not used in studies as even here the same person reports wildly varying circumferences. Methodology used in 1976 is different from that used in 2009. Here is another paper-transplant surgeons need to know this stuff so most research comes from there.
http://www.clinicajimenezacosta.com/pdf/publicacion1.pdf

Btw, difference in i inch and 2 inch pomy is 4 times hair not 2.

[DreamSheep]

I need to know these numbers for other reasons than just curiosity and here is an old paper that maybe helpful.
http://journal.scconline.org/pdf/cc1977/cc028n05/p00219-p00230.pdf

Ponytail measurement is layperson's method and is not used in studies as even here the same person reports wildly varying circumferences. Methodology used in 1976 is different from that used in 2009. Here is another paper-transplant surgeons need to know this stuff so most research comes from there.
http://www.clinicajimenezacosta.com/pdf/publicacion1.pdf

Btw, difference in i inch and 2 inch pomy is 4 times hair not 2.

Thank you! :D All of this makes me very happy!