There are precisely 28.3495231 grams in one ounce. This number is commonly rounded to 28 for easier conversions. The gram is the base unit of mass or weight in the metric system, and the ounce is a unit of weight in the U.S. customary system.
To convert a measurement in ounces to an approximate number of grams, multiply it by the factor 28. Conversely, to convert a measurement in grams to ounces, divide it by the divisor 28. Although ounces are the preferred measurement in the United States, grams are used by most of the world and in all scientific applications.