What length!

[aris]

I would have thought one could use a device similar to what jewlers use to measure ring sizes. Otherwise, doing a bit of math, one could figure out the equivalent size when you measure the casing flat.

[sausagemaker]

Except the casing isn't flat when its produced it's full of ****

[TobyB]

measured flat and then doubled would give you an (approximate) circumference.

Given that natural casings are not uniform along their length I personally can't see the point. I just do roughly as much as I think I'm going to need and then a bit extra to allow for my errors. They aren't exactly expensive so if I end up throwing away the odd foot or two I don't get too excited (and you could always re-salt them if you are feeling frugal)... mind you, the other day I ran out with about a pound of meat still to go and didn't have any more (salted or rinsed) spare so had to make burgers. You live and learn as they say

[aris]

Same happened to me - I ran out.

I usually fall back to collagen casings, or cheat a bit and quickly soak and rinse through a hog casing with some warm water.