For grommet curtains you will need to take into account the placement of the grommet.
Height to put curtain rod.
Go high a rule of thumb from architectural digest is that curtains should be hung between 4 to 6 inches above the window frame so install your curtain rod accordingly.
For standard drapes that hang on either side of a window the typical height is halfway between the top of the window.
When you hang the curtain rod high it will make the window appear taller.
For cathedral ceilings leave approximately four to six inches above the window trim as a guideline.
This is a traditional height though you can cheat an inch or so either way depending on the height of your ceiling and the length of your finished curtains.
Don t scrimp on length.
Make a mark about four inches above your window for mounting hardware.