In various implementations, an adjustable dumbbell system may include a handle assembly, two or more weight plates, and a base. The weight plates and the handle assembly may be configured such that each weight plate can be selectively coupled to and decoupled from the handle assembly. The base may be configured to support each of the weight plates. The base may include a sensing mechanism that senses a characteristic of the weight plates where the characteristic depends upon which of the weight plates are supported by the base.