Oz/ɑz/ Definition 1 of 5Pro Tip 1/3Measurement Clarification Remember 'oz' for weight is different from 'fl oz' which measures volume. The perfume is 3 oz, not fl oz. Pro Tip 2/3Imperial vs. Metric Oz is used in the Imperial system; most countries use grams. Ingredients may list 100g alongside 3.5 oz. Pro Tip 3/3Cultural Usage In the US, 'oz' is common in recipes and on packaged goods. This snack comes in 5 oz bags.