Multidimensional Scale of Perceived Social Support (MSPSS)
The Multidimensional Scale of Perceived Social Support (MSPSS) is a self-report measure of subjectively assessed social support. This 12-item instrument uses a 5-point Likert scale. It also has 3 subscales: significant other, family, and friends.
The linked article includes the MSPSS itself as well as its documentation, including its development, validity tests, and reliability tests.
Authors provide instrument validity and/or reliability information.