A method according to one embodiment includes selecting an initial radius value (Rfull) for an outgoing reel, where Rfull is the initial radius of a tape on the outgoing reel; unwinding the tape from the outgoing reel; computing a radius value of the tape on the outgoing reel during the unwinding; adjusting the computed radius with an offset calculated from a direct measurement of velocity from the tape position; and outputting the adjusted computed radius. A method according to another embodiment includes selecting an initial radius value (R0) for an incoming reel, where R0 is the initial radius of the incoming reel; winding the tape onto the incoming reel; computing a radius value of the tape on the incoming reel during the winding; adjusting the computed radius with an offset calculated from a direct measurement of velocity from the tape position; and outputting the adjusted computed radius.