measuring rough opening

I was told to get rough opening measurements for replacement windows, that you need to measure the length and width of the opening where the 2x4's are . how can you do this with the window still installed?

one place told me that to get the proper measurements of the rough opening that you would take the window out first.

I took the inside molding around the window off and measured the total length and width of the window that's installed right now. I don't believe that these measurements I get are close to Windows that I see for sale.

these windows were installed in 1975 and I want to replace with double hung vinyl windows.

Thanks for any input
Randy

 

Who told you to get the rough openings? Who's supplying the windows? Who will be installing them?

The rough opening is simply the size of hole that was framed into the wall when it was built. Assuming that you have 1/2" sheetrock installed on the walls, you can simply measure the width of the opening inside and add an inch -- that will be the rough opening width. Getting the height can be trickier, depending on what was used on the sill. If it's 1/2" sheetrock, just measure the height of the inside opening and add an inch. But, you may have a metal sill plate -- in that case you only want to add 1/2" (for the sheetrock on the header).

New construction windows are generally done in 6" incriments. If you measure an inside opening that is 47" wide and 35" tall, your rough opening is 4/0-3/0.