To determine the width of your shutter, divide the width of the window
opening in half. For short windows where the height is smaller than
the width, divide the width of the window by 4.
The height of the shutter is usually the
height of the opening, not counting the window sill.
For double windows, divide the opening width by 4. For consistency, if
the width is close to the measurements for your single windows, use
the single width.