Abstract: An apparatus (100) for measuring body fat mass and degree of obesity of a person (P) is provided. According to one aspect, the apparatus comprises a second bar (102) optionally configured to be placed on a horizontal surface, and a first bar (101) configured to be movable along and being perpendicular to said second bar (102) and an optional control unit (111). A first connecting means (105) connects said first bar (101) to said second bar (102). A light emitting device (104) is connected to said first sliding member (103) and is configured to emit light in a direction perpendicular to the plane defined by the first and second bar (101, 102).