Ounce/aʊns/ Definition 1 of 4Pro Tip 1/3Standard Measurement An ounce is commonly used in the U.S. for cooking and measuring body weight. The newborn baby weighed six pounds and five ounces. Pro Tip 2/3Imperial vs Metric An ounce is part of the imperial system, so it's less known in countries using the metric system. He understands kilograms better than ounces. Pro Tip 3/3Different from Ounces Don’t confuse 'ounce' with 'ounces,' which is simply the plural form. Just add two ounces of sugar to the mix.