Denier or den is a unit of measure for the linear mass density of fibers. It is defined as the mass in grams per 9,000 meters. In the International System of Units the tex is used instead (see below). The denier is based on a natural standard: a single strand of silk is approximately one denier. A 9,000-meter strand of silk weighs about one gram. The term denier is from the French denier, a coin of small value (worth 1/12 of a sou). Applied to yarn, a denier was held to be equal in weight to 1/24 of an ounce. The term microdenier is used to describe filaments that weigh less than one gram per 9,000 meter length.