Geometry conversion from compact sloping frame

Hi everyone,

Not sure if I'm in the right forum. If not, I apologize, and I'd appreciate directing me to the right forum.

I am wondering about the following: if a compact sloping frame has a 42cm seat-tube length, I imagine it does not automatically mean I'll need a 42cm size regular frame, correct? By "regular", I meant non-sloping traditional horizontal frame.

Follow-on question: how do I, if it's possible, convert the measurements of such a compact sloping frame into a regular frame? That is, can the geometry of a compact sloping frame tell me what geometry I'd need in a regular traditional horizontal frame in order to achieve similar fit?

Thanks very much!

Jack