In roll forming, flat strip is progressively deformed by sets of rotating rolls; it is a commercially important metal forming process but not one that has been extensively studied on a scientific basis. This paper introduces a new method of indicating forming severity, the bend angle curve, which shows the bend angle distribution and the geometric restrictions imposed by the shape of the rolls, it includes and extends an existing theoretical model of deformation in the unsupported strip based on a modified minimum energy concept. Experiments were carried out in which a channel section was roll-formed and the shape of the strip measured along the whole deformation region. Good correlation was obtained with the predicted bending angle curve and the results demonstrate the influence of roll diameter as well as cross-sectional shape.