The method of accurately measuring the volume of urine in a bladder includes generating a plurality of ultrasound scan planes using the received ultrasound signals detecting distances between the front and back walls of the bladder for each scan line in the ultrasound scan planes determining an area of the bladder using the detected distances of the scan lines for each ultrasound scan plane generating a virtual radius of the bladder using the determined area of the bladder for each ultrasound scan plane determining a calibration coefficient for each ultrasound scan plane using the detected distances of the scan lines calibrating the virtual radius of the bladder for each ultrasound scan plane using the calibration coefficient determining the volume of urine in the bladder by calculating the volume of a sphere of which the radius is the average of the calibrated virtual radii for the ultrasound scan planes.
