Mg/kg means milligrams per kilogram, and is the unit of measurement we use to measure pesticides in food. When we say we found 1 mg/kg of a pesticide in a food, this means that for every kilogram of food we tested we found 1 mg of pesticide. There are 1000 milligrams in a gram, and 1000 grams in a kilogram. So there are a million (one thousand, thousand) milligrams in a kilogram. Another way of expressing milligrams per kilogram is parts per million so 1 milligram per kilogram is one part per million