In the beginning
The most important thing was to measure.
1. Measure the width. The lady’s window was 35″ wide. They determined how far past the window is wide. They added 4″ to each side of the width measurement. They had to take into consideration the width of the curtain rod and the fluff of the curtains. The rod went just past the frame.
2. After that they measured the depth. Now, if you hang curtains under your board you need to figure for the rod. They used a 2″ curtain rod (it came off the wall 2″).
The woman wanted about 1″ clearance past the rod and then she added 1″ for the curtains. So to add it all up 2″ rod + 1″ curtain + 1″ clearance past that = 4″ for the depth of her boards.
3. Determine how long you want your boards to be. The standard seems to be to take the length of your window or window coverings in this case, divide that amount by 5 and take 1/5 as the length of your boards. Her window coverings were 82″ so she came up with a little over 16″ and decided on 17″.