Method, apparatus, and systems for roll angle estimation for an input/gesture device (IGD) are disclosed. The method includes estimating a first axis vector of the input/gesture device (IGD) relative to the surface of the mobile device (MD), as a first frame of reference, using readings from a first type of sensor; and estimating the first axis vector of the IDG relative to a different, second frame of reference using a gyroscope integration of readings from the 3-axis gyroscope. The method further includes aligning the first axis vector of the IDG in the first frame of reference with the first axis vector of the IDG in the second frame of reference; minimizing a change in the alignment of the first axis vectors between the first frame of reference and the second frame of reference; and determining the roll angle of the IDG relative to the surface of the MD.