kg is the written short form of kilogram or kilograms, the usual unit for how heavy something is. A bag of rice, a person’s weight, a suitcase at the airport: these are often written in kg. You see it on packets, on scales, and in maths. When we speak, we usually say “kilogram” or “kilo,” not the letters; the letters are mainly for writing. It is the international symbol, so it is written kg in small letters, and we do not add an s: 3 kg, not 3 kgs. Though actually, people do write kgs in casual notes, but that is not the correct symbol. One kilogram is 1,000 grams. Do not mix kg with km (kilometre, for distance) or with lb (pounds, still common in the US).