What is a carat?
A metric carat is 200 milligrams (0.2 grams), the unit gemstones and pearls are weighed in. Karat with a K, which measures gold purity, is a different thing.
What is a kilogram?
A kilogram is metric unit of weight subdivided into 1,000 grams. The base unit of mass in the International System of Units (SI) is a kilogram and not, as is quite often mistaken, the gram.
One liter of water weighs 1kg.