Calculating size of tam top

How big to make the top of tam?


To make the pattern for the tam, you first need to figure out how big the top of the tam will be.

In terms of our tam pattern, the top of the tam is the inner octagon, inscribed in the circle BCDEFGHI (figure 1).  So the question is, what is the RADIUS of that circle?

Figure 1

Short answer:  

The RADIUS of that circle should be BRIM WIDTH + radius of hat band seam.

Longer answer:

The radius of the top should, of course, be larger than the radius of the hat band seam (and the difference should be the width of the brim).  How wide should the brim be?  My guesstimate (looking at pictures) is that it should be at least 3", if the hat is going to sit low enough on the head for the band to attach to the head.     (It turns out this is way too big)

Here are some examples:


  • Suppose the tam is 12" across  That would make the RADIUS of the outer octagon (Figure 1) = 6". With a brim of  3", that would make the radius of the hat band seam 18.8" (child-size, as in Figure 2):

Figure 2


  • My own head measurement, on the other hand, is about 23" circumference (= radius 3.7). Adding in the thickness of the brim material (estimate .25") the radius of the hatband seam would be nearly 4". If you add a 3" brim to that, then the radius of the tam top for me would be 7" (that is, 14" across):

Figure 3

  • If your head measures 21" around (radius 3.3"), then the radius of the band seam will be approx 3.6", and with a 3" brim that would yield a tam top radius of 6.6", or 13" across.


Remember: the top width (tam diameter) is the inner octagon of the pattern (Figure 1), so the PATTERN WIDTH will the double the tam diameter.  In these examples:
Head Measurement
Tam Diameter
Pattern Width
18”
12”
24”
21”
13”
26”
23”
14”
28”



I will have to try this out to confirm:




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