The present inventions, in one aspect, are directed to a portable monitoring device to calculate a number of stairs or flights of stairs traversed by a user, the portable monitoring device comprising (i) a motion sensor to detect motion of the user and, in response thereto, to generate data which is representative of motion of the user, (ii) an altitude sensor to detect a change in altitude of the user and, in response thereto, to generate data which is representative of the change in altitude of the user, and (iii) processing circuitry, coupled to the motion sensor and the altitude sensor, to calculate a number of stairs or flights of stairs traversed by the user using the data which is representative of motion of the user and the data which is representative of a change in altitude of the user. The portable monitoring device may include a housing having a physical size and shape that is adapted to couple to the body of the user.