Given length and width...

[Glass Shark]

Hi all. I have been lurking (something I do very well ) here in the lounge for a couple of months and thought I would make my presence known. This site has become one of my favorites and I have learned a thing or two from the wealth of information you fine folks have. I appreciate your sharing.

Something I have noticed, while perusing OFAS, is the tendency of sellers to list the length and width of the hat opening instead of the circumference. Undoubtedly, they assume a large sector of their target market are or were math majors at university. Length and width measurements were of little use to me until I found this website:

http://www.csgnetwork.com/circumellipse.html

Plug in the numbers for length and width, hit the calculate button, and it gives the circumference as the answer. I plugged in 8 and 6.75 and came up with a circumference of 23.25229. Much to large for my 7 1/8 head. Sad, so sad.

I hope this has been of some help. You good people have been a great help to me.

 

[HarpPlayerGene]

Welcome!

Thanks for that link. I usually go by circumference measurements but often they are harder for the seller to get right. Also, I am a Long Oval and sometimes it's actually helpful to have the length/width measurement. In my collection of hats, there are a couple that really fit well, so I just measured the length/width of those and that way I know what will work for me when I'm on the hunt for a new addition.

 

[KY Gentleman]

Welcome to the Lounge, Glass Shark! Thank you for the info.

 

[deanglen]

Greetings, GlassShark, good to have you with us. Great idea on the calculations there. Helps when browsing listings!






dean

 

[Woodfluter]

///Something I have noticed, while perusing OFAS, is the tendency of sellers to list the length and width of the hat opening instead of the circumference. Undoubtedly, they assume a large sector of their target market are or were math majors at university. Length and width measurements were of little use to me until I found this website:

http://www.csgnetwork.com/circumellipse.html

Plug in the numbers for length and width, hit the calculate button, and it gives the circumference as the answer. I plugged in 8 and 6.75 and came up with a circumference of 23.25229

Hi Glass Shark and welcome!

This was something I meant to look into myself, but hadn't.

However, it would seem easier at times to do the calculation with a simple equation rather than going back to that site. The equation they give doesn't agree well with the results of the Javascript routine. For an arbitrary example, if I plug in a long axis of 8 and short axis of 5, it gives me 20.96 which is in the ballpark.

The equation they give is (using a for maximum radius and b for minimum radius instead of diameters, for uniformity) C = 2 pi (a^2 + b^2)^0.5
and for the example I gave, that works out to 29.63! Also I can't find reference to anything like this equation, nor as simple.

For the range of values we'd encounter (low eccentricity), the 1st Ramanujan approximation is considered very accurate:
C = pi*(3(a+b) - [(a+3b)(3a+b)]^0.5)
That gives a circumference of 20.69 for the 8 by 5 example.

Real World Reality Check:

My Akubra Fed IV: diameters 206 x 167 mm, C = 58.75 cm (or 58.9 per your site)
Now that's a bit of a puzzle. It is listed as a 60, but I've shrunk it down slightly at the base of the crown because I'm in between a 59 and 60. Still, the calculated value just doesn't jive with the fact that most hats marked 59 or 7-3/8 are too tight on me! And this hat is not.

Let's try a vintage Stetson Royal marked as 7-1/2 long oval, which fits me perfectly. Diameters 210 x 167 mm, C = 59.4 cm (or 59.6 per your site). That still isn't a size 60. However, it might account for it fitting my very long oval head with an in-between size so well! Could have shrunk a half size over the years?

Well, hope this helps and my apologies for the math.

- Bill

 

[Glass Shark]

Thank you

Thank you all for the kind words of welcome.

Woodfluter, thank you for pointing out that the forum members would be better served by using the Ramanujan formula. The following calculator is based on that formula:

http://www.cleavebooks.co.uk/scol/callipse.htm

Please understand that the calculation is an approximate circumference. It may give you enough of a ballpark figure to guide your bidding.

Also, we must allow for the sellers ability to measure properly. Case in point: "The hat measures 22 inches around and is 8 1/2 inches long by 7 inches wide." The calculator shows a circumference of 24.4 inches. I have no idea the size of this hat!

Guido

 

[Colby Jack]

Welcome to the lounge Glass Shark!:eusa_clap :eusa_clap :eusa_clap