Small linear dipole antennas with a multi-band characteristic are necessary for many strip or bar shaped gateway devices of the Internet of Things (IoT), for the connectivity in various communication protocols. However, the conventional methodology of designing multi-band dipole antennas is generally empirically based. More frequency bands usually mean even more arms/slots, which results in an increasingly bulky antenna. In this paper, we will introduce an algorithm of using the fewest arms to design a multi-band linear dipole antenna. This algorithm is based on sharing arms after the effective ranges of mode excitation are determined by characteristic mode analysis (CMA). By this algorithm, an exemplified designed penta-band dipole antenna is effective in covering 433, 868, 1176, 1575, and 2450 MHz bands for LPWAN, GNSS, and ISM applications, with only 2.5 pairs of arms. 50% of arms are reduced in comparison to traditional methods. This algorithm is convenient in practical dipole antenna design, and greatly simplifies the antenna structure so that they could be mounted into small IoT devices.