I did roll it out in my garage and measured it in 20' or so incremeents (it's about 150' long) but wanted to double check.

The only online calculators I could find (and there was a bunch) wanted inner and outer diameter.... and material thickness.

a) I don't know the thickness

b) seems that depending on how tightly rolled the item is, that will change the outer diameter / affect calculated result.

My thinking is that the number of wraps, OD and ID would work, but can't find a calculator for that. Any recommendations? Is that more of a calculus formula (I'm 57... I really don't remember calc other than the s shaped symbol? Or was that differential equations : )

But my thinking is that if you do it by hand you would do repeated circumference calculations using slightly larger diameters each time (and you'd be doing that x times where x= number of wraps?

Or you find the 'average diameter (or is it the mean? median?)', find the circumference there and multiply by the number of wraps? And the diameter i am thinking of is the midpoint of the material - the same length of material from there to the OD as from there to the ID. Would saying same area be a safe approximation? for a 5=od and 1.875 ID, I came up with diameter of 3.8 for same area above and below that diameter?

Is that another way to do it? Is 3.8" correct?

Should i roll it out on the driveway rather than use math : )