I’d say you want the same size window or downsize it to fit inside the sheetrock opening and downsize it. all depends in how yoy mount it.

For sure won’t be installing myself but need an idea of what to even shop for, I guess it’s the new construction label vs replacement and other terms that leave me realizing I don’t know what I am looking for.

I second the comment to get an installer to measure, and one who is very experienced with windows.

I had some measured and replaced by a general contractor. It took a lot of caulk to fill in between the new window and the old opening. I had others replaced by a window replacement company. They ordered the windows much closer to the opening size and the windows fit with little room to spare.

A replacement window is for when you are keeping the existing jambs (typically). In your case you are altering the opening so you need a new construction window. The way to accurately measure is to remove the interior trim so you can fit to the overall rough opening. At that point you will verify that the header is continuous (it should be but old houses can be wacky)

Thank you! This is what I was looking for, addressing the amount of trim and if that counts in the measurements!!

New construction windows involves redoing the trim inside and out.

There are going to be multiple ways to install new windows here, each with some pros and cons from price, to larger size/more glass, more protection against future leakage, etc. This is a conversation to have with the companies that you have quote the project for you, as the type of install can affect the price substantially. Just beacuse your home is not "new", it doesn't mean that they windows couldn't still be installed as "new construction".

No accurate measurements would be needed or really even relevant by you, but again discussing the install details and the ramifications of those options -- particulalry as it pertains to the size based on your concern should provide the info that you are looking for.

In the event that you are considering doing this install yourself, I'd recommend some serious research on installation methods and procedures. You really can't measure a window properly unless you understand how its going to be installed.

When we replaced windows in our house, the window company did all the measuring - once to give me a bid, and again before he placed the order. They also did the install.

Did anyone confirm if that mull cover has a load bearing timber strand in it.