The invention provides a device for selecting a size by body measurement. The device comprises a foot length measurement device, a measurement control unit and a control device, wherein the foot length measurement device comprises a pedal, a positioning part, a measurement plate and a distance-measuring sensor; the measurement control unit is respectively and electrically connected with the positioning part and the distance-measuring sensor and used for receiving a foot length measurement triggering signal to control the distance-measuring sensor for carrying out distance measurement and calculating a foot length value according to the measurement value of the distance-measuring sensor; and the control device comprises a shoe size selecting unit, wherein the shoe size selecting unit is used for receiving the foot length value sent by the measurement control unit so as to compute a shoe size. According to the device disclosed by the invention, no tape measure is need for measurement, the proper shoe size can be quickly and accurately selected, and the characteristics of high efficiency and high accuracy are achieved. In addition, a non-contact human body three-dimensional measurement technology is not needed, and the measurement of the foot length can be realized only through simple mechanisms. Thus, the device for selecting the size by body measurement, disclosed by the invention, also has the characteristics of simple structure, convenience for operation and low cost.