Lesson Eight: Chemical Dosage Terminology

Chemical dosages for water treatment chemicals are expressed as milligrams-per-liter (mg/l). Milligrams-per-liter are often refered to as parts-per-million (ppm). One mg/l is exactly equal to one ppm.
Chemical dosages are actually a ratio of the weight of the chemical to the weight of the water. In the metric system, one liter of water weighs exactly 1000 grams. In the metric system, one milligram weighs exactly one-thousandth of one gram. Since there are one thousand milligrams in one gram and there are one thousand grams in one liter of water, there are one million milligrams in a liter of water. If a chemical compound is present in a liter of water at a weigh of one milligram, it is present at one ppm.