Loneliness Scale
Feeling lonely is perhaps the single biggest determinant of a host of psychological and physiological illnesses, ranging from depression and insomnia to obesity and diabetes. Interestingly, it is perceived (and not actual) loneliness that matters, and given its significance for happiness, you can fill out this scale and know more about your perceived loneliness levels.
The scale was developed by Daniel W. Russell (1996) and has twenty items. About half the items are worded in a way that probes what you feel is missing from your life, while the other half probes what you feel is present.