A king size bed is 76" wide x 80 long. For a headboard, I'd conservatively add 3" per side, bringing it to 82" wide but that could be more depending on the headboard. I believe ours is closer to 86" wide. Nightstands are a total unknown because you don't have them yet and they could be as small as a 15" wide table or as large as double chest of drawers. We don't have matching nightstands but each is approximately 36" wide. Our headboard overhangs the window trim in our room just a bit because we planned it for a queen bed - live and learn. Our nightstands sit in front of the windows on that wall. With a bed width at 86" and nightstand at 36" and you want a few inches of breathing room between the bed and nightstands ....... you would need roughly 10 - 12 feet BETWEEN the windows if you don't want the nightstands in front of the windows at all. Then, you don't want the windows shoved into the corner so need space from the window to adjoining wall. Do you have that kind of space in your proposed MBr?

too many variables to know. A king size mattress is about 76" wide -say 80" with frame. The windows would look best centered on the nightstands which are generally 24-30 inches.

So we can use 30" + 80" (+ 2" for insurance) than the windows would be 112" on center.

This would give you a pretty good range of possible furniture on the smaller scale side.

If your plans are to scale then looking to the left you have a 7' dimension drawn and without measuring it looks like you don't have much more than 7' between windows.

The width of the wall is 19'11"

Why would you want the upper story windows not in line with the first floor?

LOTO i could align the downstairs windows once i get the right distance set in the MBR.