You will never know exactly what the string tension is for your racket, especially if you are not the one who strings your racket. Even if you string your racket yourself, you are only sure about the set tension. However, if you string enough rackets, you will have a good estimation on what the tension of a racket. Cheers.
The BG #numbers are the types of strings and not the tension. The tension of a racquet is when you actually string the racquet.