Is inside the frame (i.e. the visible portion) correct?
To Measure Width:
Measure between the jambs at three points: top, middle and bottom of the window opening. Measure from the surface of the jambs, not from the trim strips or parting beads in your old window opening. Use the smallest of these three measurements to order the window.
To Measure Height:
Measure from the high point of the sill of your window (the surface closest to the inside of the window) to the top of the window opening. Make three measurements: one at the left side, one at the center and one at the right side of the window. Use the smallest of these three height measurements to order the window.
To Measure Depth:
Ignore all pulleys and parting strips when measuring for depth dimensions, as they’ll be removed for replacement window installation. There must be at least 3 1/4 inches of opening depth between the inside window trim and the outside blind stop strip. This much area is necessary to accept the depth of the replacement window.
You measure a window for actual size say 24"x48" and the framing will always be 1 inch or more taller in height and 2 inches in width which is called a rough opening. So again there is always two measurements finished opening or actual size of window and rough opening what you frame the window to. It will always be finished when you are ordering from a vendor.