vinyl replacement windows

Hi Guys,
I’m getting ready to replace some old windows with vinyl replacements. I’m not totally sure how to measure for them… They will be installed into a brick opening. If you take the measurement of the brick opening, how much smaller from this measurment should the exterior dimensions of the window jamb be? I know I’ll probably have to secure 1 X’s into the brick so I have something to secure the new window, as well as some room for shims…
Also, I think the brick moulding can be ripped and installed to make up the difference between the window and the brick???
Has anyone done this type of job recently?
thanks,
-dan

Take 3 measurements on each linear suface to check for squareness ,if those are off go with the smaller #.Typically I measure the opening then take away an inch.You can always fur out more but if it does’nt fit the whole you’re stuck.Best of luck.

thanks sellnbama…