The present inventions, in one aspect, are directed to a portable activity monitoring device to calculate a number of stairs or flights of stairs traversed by a user, the monitoring device comprising (i) a housing having a physical size and shape that is adapted to couple to the body of the user, (ii) an altitude sensor, disposed in the housing, 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, disposed in the housing and 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 a change in altitude of the user.