There are two aspects to the problem. The easiest is measurement. The various definitions very roughly ranked (your mileage may vary as they say) from least to most ‘accurate’ (or more accurately, most repeatable) are:
Calculated (such as by Wound Roll Sizer app)
Number of sheeted products
Footage counter running on product
Idler roller rotations with target or tachometer
Driven roller rotations with motor tachometer
LDA (Laser Doppler Anemometry)
Complications beyond mere measurement are, well, more complicated. However, they are explained in detail in my Web101 Winding course such as coming up in August 23-26 in Patterson NJ or as video-on-demand.