Method and system for determining a length of an object using an electronic device

A smart belt apparatus for providing information that is used to provide a service regarding a body of a user, the smart belt apparatus comprising:

• a communication interface configured to transmit or receive data to or from an external device;
• at least one first sensor configured to sense that the smart belt apparatus is being worn by the user;
• at least one second sensor configured to sense a movement of the user;
• and
• a processor configured to, in response to the at least one first sensor sensing that the smart belt apparatus is being worn by the user, make a determination whether a current posture of the user is a reference posture that is pre-defined, measure a waist size of the user by using the at least one first sensor, correct the measured waist size based on the determination, sense a motion of the user by using the at least one second sensor, and provide information about the measured waist size of the user and information about the sensed motion to the external device via the communication interface,
• wherein the processor is further configured to:
• correct the measured waist size based on a first tension value corresponding to the reference posture based on a determination that the current posture of the user is the reference posture;
• and
• correct the measured waist size based on a second tension value estimated from the first tension value by using a human body modeling information based on a determination that the current posture of the user is not the reference posture.