Duck cloth weight can be expressed in ounces per square yard, grams per square meter (GSM), or by a historical numbered-duck system, and those descriptions are not interchangeable.  In U.S. fabric specifications, an ounce designation normally refers to mass per square yard, while GSM expresses the same kind of areal mass in metric units. Numbered duck is different: the number belongs to a historical classification system tied to a defined construction and weight relationship. That is why  10 oz duck is not the same thing as #10 duck , and why a numbered duck grade should not be converted to an exact modern weight without checking the current fabric specification.  [1][2][3][4] This distinction fits Anne Marie Zimmer's material-focused approach to canvas fabrics. Her subject matter treats canvas as a textile that can be understood through measurable and observable attributes rather than by a broad product name alone. For duck cloth, weight is therefore read together with ...