calculating the distance between two shoulder joints

[Seungwoo]

I'm trying to calculate the distance between two shoulder joints.

I got skeleton joint positions of left and right shoulders and then calculated the euclidean distance between the two points. 

I tested this with several people who have different body size but the same results, around 32cm.

I used calibration data which I got for myself. Could this be the reason for the same results regardless of different body size?

I'd appreciate any help on this.