Interestingly , IELTS is a multi-level exam and bands are classified on a scale of 3-9 for certain scores. Overall, bands are final product of adding bands scored in all four sections (LRWS ) divided by no of sections (4)
For instance , if candidate has scored
L- 7, R - 6.5 , W- 6.5 , S -6
So this will be added ,
7+6.5+6.5+6 = 26 which will be divided by 4
26\4 = 6.5 bands
Overall bands = 6.5