Since 1 pound is equal to 453.59237 grams, or 0.45359 kilograms, 173 pounds would be equal to 78.47 kilograms. Conversely, 1 kilogram is equal to 2.2046 pounds. Each kilogram is comprised of 1,000 grams, while each pound is comprised of 16 ounces.
The kilogram is used to measure mass in the metric system, and 1 kilogram is equal to the mass of 1 liter of water. The metric system is used in most of the world, with the United States, Canada and the United Kingdom being the notable exceptions; these countries most frequently use pounds and ounces to measure mass. The metric system was constructed and published in France in 1795.