Abstract: A volumetric measuring device for measuring a body part. The device includes a fluid container filled with fluid. The fluid container has a body part opening for permitting the insertion of a body part and a displaced fluid opening for permitting the flow of fluid that has been displaced as the result of inserting the body part. A watertight barrier covers the body part opening and maintains a watertight seal over the body part opening while the body part is being inserted. The volumetric measurement is determined by measuring the amount of displaced fluid after the insertion of the body part through the body part opening. In a preferred embodiment, the body part being measured is an erect penis.