The bias (US) or cross-grain (UK) direction of a piece of woven fabric, usually referred to simply as "the bias" or "the cross-grain", is at 45 degrees to its warp and weft threads. Every piece of woven fabric has two biases, perpendicular to each other.

Woven fabric is more elastic as well as more fluid in the bias direction, compared to the on-grain direction. This property facilitates garments and garment details that require extra elasticity or drapability or flexibility, such as bias-cut skirts and dresses, neckties, piping trims and decorations, bound seams, etc.

A garment made of woven fabric is said to be "cut on the bias" when the fabric's warp and weft threads are at 45 degrees to its major seam lines.