A couple of years ago I wanted to make some Taylor Pork Roll and I needed the cotton casings. Couldn't find any sources on line so I looked up sources for Unbleached Muslin and some handy dandy formulas to calculate what size to cut the material to get the diameter I wanted. I bought the fabric from the link shown at the bottom. The price was reasonable, I bought 10 yards of the 48" wide fabric for about $2.45 a yard plus shipping which was also reasonable.
I made multiple diameter sizes for different kinds of sausages, a large quantity of each, and I still have plenty of muslin left over. I don't think that I will ever use all of it. I checked my notes and the formulae for the bags is as follows:
Circumference = pi D = 3.14 x Dia
Circumference = 2pi R = 6.28 x Radius
5” Dia, C = 3.14 x 5” = 15.7” + 1 inch for Seam 16.7”
4” Dia, C = 3.14 x 4” = 12.56” + 1 inch for Seam 13.6”
3” Dia, C = 3.14 x 3” = 9.42” + 1 inch for Seam 10.5”
Make each Casing 16” long
Note: Commercial Taylor pork roll does not use the extra material for a seam. Their casing is sewn edge to edge without the extra inch. This undoubtedly saves them a lot of material.
The on line store is