3mg/ml or 0.3% (Lowest with nicotine) - suitable if you are smoking 5 a day . 6mg/ml or 0.6% (Low) - suitable if you are smoking 5 to 10 a day. 12mg/ml or 1.2% (Medium) - suitable if you are smoking 10 to 15 a day. 18mg/ml or 1.8% (High) - suitable if you are smoking 20 to 30 a day.