How To Measure A Shutter
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.
Divide the opening width by 6.