Rough-in for a beginner

So I am getting ready to redo two of my bathrooms. I am looking at the Toto Aquia, but I might be getting ahead of myself since I'm not sure how to assess if I even have enough space to make this all work. What exactly do I need to measure to see I can fit this toilet in my existing space?

Am I correct in assuming that in order to get the rough-in measurement, I need to remove my old toilet and measure the distance from the back wall to the edge of the drain pipe?

I'm replacing a toilet from the late 70's and I can't even find a brand name on it!

Thanks in advance everyone.

Stanley

The center of the bolt caps that hold the toilet down should work.

A standard 12" rough-in measured from the wall to the center of the drain, which is where the bolts should be.