Basis weight is a very common term in the nonwovens industry. We use it to express how much a nonwoven fabric weighs per unit area. The term comes from the papermaking industry. In most areas of the world basis weight is expressed as grams per square meter. In the United States, lightweight nonwovens such as diaper cover stock may use grams per square meter and some companies even mix the metric and English systems and express basis weight as grams per square yard. In heaver fabrics such as needlepunch, the basis weight is often given in ounces per square yard. Fabric samples are rarely a full square yard or meter. Usually the fabric is folded in such a way that small samples are taken across the web to see weight variations. These samples are often punched out with a clicker press as shown in the photo. The samples are then weighed on an accurate digital scale and the weight for a square yard or meter is calculated. Basis weight is a snapshot of the fabric weight whereas derived weight is calculated by weighting a roll of finished fabric and determining the basis weight for the entire roll by dividing total roll weight by the number of square yards or square meters on the roll. Derived weight cannot show variations within the roll.