Regular windows

How would you measure regular windows that were put in 60 years ago, and need to be replaced?

 

that depends on whether you are completely tearing out the old windows, and will be installing a "new construction" window, which has a nailing fin, then retrimming the inside and outside of the window -or- whether you are asking how to measure for replacement windows, which are meant to fit inside the old window frame once the old window sashes have been removed. Replacement windows are desirable for some because they do not usually entail as much work / cost. However, total replacement is often the "best" method if you can afford it.

 

What Sleeper said. Replacement window measurements involve width, height, and measure for square. Ideally, measure the frame at 3 points on both width/height, and diagonally(square).

For rough frame opening for new construction windows, it is usually necessary to remove the inside trim to see the framing. And the exterior finish will have a big impact on the cost. Vinyl siding is easy to remove and reinstall, brick is not.

Most of my clients can't afford new construction windows, so replacement windows are fine. They will save roughly 15-30% in fuel over single glazed windows. But they usually reduce the clear glass opening, something some people do not like. In this case, consider a sash replacement kit like Marvin TiltPac.