DSLRs usually don’t list a single “zoom ratio” because zoom is a property of the lens, not the camera body. Since DSLRs use interchangeable lenses, the camera itself may be used with anything from a fixed focal length lens to many different zoom lenses.

For a zoom lens, the zoom ratio is simply:

longest focal length ÷ shortest focal length

Example: a 10–100mm lens is a 10x zoom.

That said, the “x zoom” number is often not very useful by itself. A 5–50mm lens is also 10x, but it behaves very differently from a 70–400mm lens, which is only about 5.7x. What matters more in photography is the actual focal length range, and also sensor size when comparing angle of view between cameras.

So when looking at DSLR or mirrorless gear, check the lens focal length (for example, 18–55mm or 70–200mm) rather than looking for an “x zoom” number. Higher-end gear usually uses focal length specs because they are more informative than a marketing-style zoom ratio.