Units / equations for linear damping?

I am implementing an object on a spring into my project, and I am attempting to set the linear damping of the object such that the object’s motion is critically damped. In other words, the object will spring to rest as quickly as possible without oscillating.

I would like to be able to calculate a value for Linear Damping based on the object’s mass. However, there are no units on this value and I can find nothing online explaining the equations which use this value.

Can someone please tell me the relationship between the Linear Damping value and the drag force applied? Or explain why what I am trying is not possible?