An adjustable dumbbell system having a weight sensor is provided. The adjustable dumbbell system may include a handle assembly, a plurality of weights selectively fixedly connectable to the handle assembly, a sleeve rotatably coupled to the handle assembly, an indexing wheel rotatably coupled to the handle assembly and arranged to rotate with the sleeve, at least one sensor configured to detect the rotational position of the indexing wheel, and a computing device in communication with the at least one sensor. The rotational position of the sleeve may correspond to a different combination of the plurality of weights fixedly connected to the handle assembly. The computing device may be configured to determine the different combination of the plurality of weights fixedly connected to the handle assembly based on the rotational position of the indexing wheel detected by the at least one sensor.