The development of sustainable urban areas is unattainable without considering the health and wellbeing of their residents. Outdoor thermal comfort plays a vital role therein to inform decision makers on the viability of design alternatives, climate policy and action. Although the Universal Thermal Climate Index (UTCI) has become an established tool for assessing outdoor thermal comfort, calibration of the assessment scale to improve its applicability in hot arid regions is lacking. This study utilises in-situ questionnaire surveys along with meteorological measurements to calibrate the UTCI scale for the hot arid climate of Cairo, Egypt. The methods include collecting subjective thermal perception votes of 1030 individuals while simultaneously monitoring the meteorological parameters shaping their objective sensation, the UTCI. The calibration employs three distinct techniques, with the optimal method predicting measured thermal sensations being selected based on statistical criteria. Results show that the 'no thermal stress' category ranges between 16.8 degrees C and 28.2 degrees C, indicating higher tolerance for hot, than for cold temperatures in Cairo. Females are shown to prefer cold conditions more than males, with a difference of preferred temperature of 3.6 degrees C, despite having almost the same neutral temperature. Comparative analyses show that the acceptable temperature range in hot arid, hot humid and oceanic climates is wider than in Mediterranean and tropical climates, spanning lower cold and higher heat stress thresholds than the thermal comfort subinterval of the original UTCI scale.