Method for determining the roll angle of a guidable and substantially or partially roll-stable projectile comprising control system, radio-based positioning receiver and sensor for measuring roll angular velocity, wherein the following steps are included: (a) actuation of the actuators of the projectile by the control system, included in the projectile, for manoeuvring of the projectile; (b) estimation of a first signal, the projectile control force, on the basis of the control system included in the projectile; (c) measurement of a second signal, the velocity of the projectile relative to the ground-fixed coordinate system, with the radio-based positioning receiver mounted in the projectile; (d) measurement of a third signal, the rotational velocity, with the sensor for roll angular velocity mounted in the projectile; said method being characterized in that the following step is further included: (e) calculation of a roll angle on the basis of the first, second and third signals, estimated projectile control force, measured projectile velocity and measured rotational velocity, by summation of an absolute angle change, where the absolute angle change is set to correspond to the resultant angle of the change in pitch angle of the projectile velocity vector and the change in yaw angle of the projectile velocity vector, with weighting of an angle evaluation, where the angle evaluation is determined as a mean value of the angle of incidence evaluation, where the mean value of the angle of incidence evaluation is set to correspond to the mean value of the resultant angle of the projectile control force which controls the yaw component, β, of the angle of incidence and the projectile control force which controls the pitch component, α, of the angle of incidence. (a) actuation of the actuators of the projectile by the control system, included in the projectile, for manoeuvring of the projectile; (b) estimation of a first signal, the projectile control force, on the basis of the control system included in the projectile; (c) measurement of a second signal, the velocity of the projectile relative to the ground-fixed coordinate system, with the radio-based positioning receiver mounted in the projectile; (d) measurement of a third signal, the rotational velocity, with the sensor for roll angular velocity mounted in the projectile; said method being characterized in that the following step is further included: (e) calculation of a roll angle on the basis of the first, second and third signals, estimated projectile control force, measured projectile velocity and measured rotational velocity, by summation of an absolute angle change, where the absolute angle change is set to correspond to the resultant angle of the change in pitch angle of the projectile velocity vector and the change in yaw angle of the projectile velocity vector, with weighting of an angle evaluation, where the angle evaluation is determined as a mean value of the angle of incidence evaluation, where the mean value of the angle of incidence evaluation is set to correspond to the mean value of the resultant angle of the projectile control force which controls the yaw component, β, of the angle of incidence and the projectile control force which controls the pitch component, α, of the angle of incidence.