How do you determine the zoom for a SLR lense?

I am looking to buy a SLR, but being a beginner, I need to know how can you determine the zoom of a lens. As an example, i've been looking at a package with the Canon Rebel T3i, a 18-55mm IS lens AND a 55-250mm lens. Do you simply divide the max length by the minimum (so 250/55 = ~x4.5 ; or 55/18 = ~x3.1 )?