An apparatus and methods to quantify the volume of urine in a human bladder with a limited number of acoustic beams is disclosed. In a first version a plurality of narrow ultrasound beams is transmitted in different directions towards the bladder. Returning echoes are converted to digital form and stored in memory. A volume display on the apparatus allows to define the optimal apposition of the transducer assembly. Signal processing software automatically determines the bladder Depth D and Height H and computes the volume of urine. In a second version, a single wide angle ultrasound beam transducer transmits ultrasounds signals at a fundamental frequency to quantify the urine volume. Return signals originating from a depth beyond the usual position of the posterior wall depth of a filled bladder are analyzed for presence of higher harmonic signals, which in turn are related to the presence or absence of urine.