Healthy kidney measured. Coloured ultrasound scan showing the measurement of a normal adult kidney. This kidney (yellow, at centre) measures 98.6 millimetres; an adult kidney is usually between 10-12.5 centimetres long. They lie as a pair in the abdomen filtering the blood and excreting waste and excess water as urine. Ultrasound scans construct a picture of internal body organs by emitting high-frequency sound waves and detecting the reflections. This technique can be used to measure internal organs as well as to distinguish between healthy and abnormal tissue.