There are 2900 grams in 2.9 kilograms. The prefix "kilo" (symbol k) in the International System of Units (SI) and other systems, which denotes 10^3, it means one thousand. Therefore, there are 1,000 grams (g) in a kilogram (kg) and 0.001 kilogram equal a gram. Kilograms and grams are units of mass, not volume such as liters, gallons, quarts, pints, and cups, and can only be converted to each other if you have the specific item being measured, as each item has a different density.