20 kilograms. By the end of 2024, the thinnest person in the world is 20 kilograms. 20 kg girl KseniyaBubenko, a Russian-born girl, is 25 years old and an American female college student. She is 158cm tall and weighs only 20kg. The girl who broke the Guinness World Record caught people's attention. The thinnest person in the world is covered with bones, and there is basically no meat on his body, which gives people the feeling that it will be broken with a light touch and is very fragile.