How to calculate or convert lens mm to x times lens zoom?

Solution:
Divide the two different ‘mm’ numbers given on the lens.
For example if you have a lens with 21 – 1365 mm

21 – 1365 mm = 1365 mm divided by 21mm = 65 x zoom

Or the Canon EF 24-105mm f/4.0 L – IS USM
105 mm / 24 mm = 4,7 x zoom