Metric weight units are a system of measurement used to measure the mass or weight of an object. The three most common metric weight units are carats (6 letters), GRAMS (5 letters), and kilos (5 letters). Carats are commonly used to measure the weight of gemstones, while GRAMS are used to measure the weight of food and other small objects. Kilos are used to measure the weight of larger objects, such as luggage.