A whole-body hydration monitor detects the velocity of sound in soft tissues, which is used to determine the hydration status of a body. A set or interchangeable ultrasonic probes is provided to be easily mounted on a housing containing a controller. Each ultrasonic probe features a pair of ultrasonic transducers facing each other and spaced apart at a predetermined distance defining the acoustic base. The controller is configured to send at least one ultrasonic pulse from an emitting transducer and detect the propagation time upon arrival to the receiving transducer. Ultrasound velocity is determined using the measured propagation time and a known acoustic base of the currently connected ultrasonic probe. Magnetic connection provides for easy detachment of one probe and attachment of another with a greater or smaller acoustic base depending on the size of the muscle selected for hydration determination.
