The thickness of the web is probably insignificant compared to the roll diameter, so we can safely ignore that. Recall that the web is peeled off the outside of the roll, which is the circumference of a cylinder. That means that in 1 revolution, you get 1 circumference in length of web.
So if V = angular velocity in RPM,
and L = linear velocity in mm/min,
and D = the diameter of the roll in mm, then
L = VDπ
or, more to the point,
D = L / (Vπ)
In such situations, I always find it worthwhile to verify my logic by checking that the units work:
L / (Vπ) = (mm/min) / [(rev/min)(1/rev)] = mm
and that's a diameter measurement, so our check works.
Stephen La Rocque.>