To measure vertical blinds, measure the width and height of the window or door where they will be installed. For inside mounts, measure the width at the top, middle and bottom using the narrowest measurement. For the height, measure from the top of the opening to the bottom in three places and use the longest measurement. For outside mounts, measure the width and height of the area you want to cover, adding extra for overlap. Accurate measurements ensure a proper fit and optimal functionality.