A blown film extrusion line has an annular die gap, from which a film tube can be extruded, a flatness unit or nip rolls, which fold the film tube, a calibration basket, which is disposed between the die gap and the flatness unit or nip rolls, and which has at least two film-guide elements that guide the film tube such that the film tube retains its round cross-section, with the diameter of the film tube being adjustable by changing the relative position of the two film-guide elements. The calibration basket includes a coupling device that couples the movement of the two film-guide elements to each other.