In this paper we presented three studies with the goal of investigating the usefulness of the IOS Scale [1] for measuring relationship closeness. We conducted three studies by using comprehensive relationship inventories to test their correlations with IOS: the Relationship Closeness Inventory , the related Social Closeness Index [12] and the "We Scale" [22] (Studies 1 to 3), the Liking and Loving Scales [13] (Study 3) and the Personal Acquaintance Measure [11] (Study 3). All studies were successful in the sense that the originally reported results also hold in similar magnitude , for a non-student diverse adult population recruited via an online platform (MTurk).