mg/ml stands for milligrams of nicotine per milliliter of e-liquid. A 20 mg/ml bottle has 20 mg of nicotine in every 1 ml of liquid. To find total nicotine in a bottle, multiply the mg/ml by the bottle size in ml. For example, a 10 ml bottle at 20 mg/ml contains 200 mg of nicotine. Use the Windbar Nicotine Strength Calculator to do the math instantly.