The shutters are to look as though, if closed, they would cover your entire window. To calculate the correct size, take the width of your window and divide that by 2.
Example: a window width of 36" would best be matched with a 18" wide pair of shutters.
For double windows it is recommended to take the total window width and divide it by 4 to get your shutter width. For triple windows take the window width and divide it by 6 to get your shutter width. If you are unsure of what size shutter would look best we have some width guidelines listed below.