Measure from the top sill to the lintel. Use this measurement as the height of your shutters.
Measure the width of your window WITHOUT the trim. Make 3 measurements: top, bottom, and center. Divide the smallest measurment by 2 and that is the width for your shutters
There is a couple of things you can do.
1. Order them small enough to fit the space. (This only words for decoration. If you want them to be functional then this isn't the best option.)
2. Order Bermuda shutters. This will allow you to still have a decorative touch on the window.
Yes, take about 0.25 - 0.5 inches off the width of the window before dividing it by 2. This will allow for a gap when you shut them and also give the hinges room to operate.
Each order comes with a step-by-step instruction sheet to show you how to install your new shutters!