I always had a very difficult time measuring for curtain rod brackets, but if you take a big piece of lightweight cardboard approximately 12 x 16 inches and use it to measure for the rods instead, it will come out perfectly.
This is a super fast way to install them, as well. Place the long side of your cardboard at the ceiling, then place the bottom right side up against the side of the window and measure out and up from there, and double check from the ceiling down also, then mark - and be such to poke 2 holes where the bracket will go. To do the other side, just flip your cardboard over and you have the holes already there, just line the cardboard up with the ceiling and left side of the window.
I have used this same piece of cardboard twice now for the same sized windows in my kitchen and bedroom and this has worked great.
By CDC from FL
