Make sure you have one inch of sill space inside the window at the top for mounting. Also, make sure there’s nothing that would interfere with the shade’s functioning such as window hardware or alarms.
Measure the width inside the molding three times: at the top, at the middle, and at the bottom. Use the smallest measure for your width. Measure the height from where the shade will be installed at the top to where it will end when fully closed. Decide which side you want the cord, left or right.
Measure the width, the height, and pick either cord left or cord right.