PLEASE NOTE: You can always mix nicotine strengths to reach your prefered mg.

For example:

1 x 15ml bottle 0mg - mixed with + 1 x 15ml bottle 6mg = 30ml of 3mg
 1 x 15ml bottle 0mg - mixed with + 1 x 15ml bottle 12mg = 30m of 6mg
  1 x 15ml bottle 0mg - mixed with + 1 x 15ml bottle 18mg = 30ml of 9mg

This applies to all bottles sizes >10ml + 10ml, 15ml + 15ml, 20ml + 20ml, 30ml + 30ml.