The invention relates to a bending angle measuring method for a bending machine (1), in particular a bending press or brake press, and the bending machine (1) has a bending tool arrangement (2) with at least one upper (3) and lower tool (4). A sheet to be formed (5) is placed in the bending tool arrangement (2). A light pattern (13) is emitted onto a section by means of a lighting device (11) of a bending angle measuring device (7), the section being a single part and surrounding a sub-region on a lateral surface of the lower tool (4) and of the sheet (5) placed in the bending tool arrangement. The light pattern (13) on the lower tool (4) and on the sheet (5) is detected by an image detecting device (10) of the bending angle measuring device (7), and a bending angle is ascertained from detected light pattern (13) by an analysis module. Furthermore, a transition portion (9) between the lower tool (4) and the sheet (5) is ascertained and, based thereon, a sub-detection region (19) in the detection range (8) of the image detecting device (10) is ascertained. The sub-detection region (19) is detected by the image detecting device (10) and the currently produced bending angle is ascertained while carrying out the bending process.