A user measures a length of a target using a mobile terminal and measure a length, irrespective of time and place. The mobile terminal and the target are photographed together in front of the mirror, and a size of the target is estimated using a ratio of the pictured size versus the actual size of the mobile terminal. The actual size of the target is calculated by adjusting the estimated length with an error associated with a difference between a distance from the mirror to the mobile terminal and a distance from the mirror to the target, and thus, a length is more accurately measured. In addition, the error associated with the distance is corrected based on the photographed picture and data stored in a database and thus, a separate distance measurement sensor for correcting the distance is not required and the cost may be reduced.