SMPS Calculation

1. v₁/t₁ = v₂/t₂. (That's the easy part, used for double checking.)
2. I forget, and thus defer to experts.

SMPS transformer design is an art unto itself (and is application, frequency, SMPS topology, transformer construction, circuit layout and construction, etc, specific).

The answer is more of a general suggestion for university education and detailed study of electronics and electromagnetics (both principles and SMPS design papers, electronic SMPS controller manufacturer data sheets, a detailed internet search, etc) than a simple ohms law equation or link to a single internet application note or website.

For really simple designs you could using standard turns ratios as mentioned in post #1, but anything more complicated than the simplest low current SMPS design may result in unpredictable circuit behaviour if you don't understand the basics of SMPS design.

What's the application and SMPS current & voltage (or is this a self-learning exercise)?