Agarose hydrogels were used as a cartilage phantom to verify the feasibility of measuring the level of hydration with the speed of sound through a medium. The hydrogels of 2%, 3.4%, 4.8%, 7%, and 9.1% were placed in an apparatus designed to accurately measure the height of the hydrogel with a micrometer and the ultrasound time of flight was measured from the difference of the leading edge of the bottom and top reflections from the hydrogel. Speed of sound was calculated from the distance travelled and the observed time of flight of the sound. Modeled from a previous study, the speed of sound through the agarose hydrogels was measured and observed to have an approximately linear relationship with the water content, and the mechanical properties of the hydrogel was associated with a poroelastic model.