Carbon dioxide included in exhaled breath is often used as a tracer gas when estimation of ventilation aspect in buildings with occupants is performed. Carbon dioxide produced by occupants is the key for the estimation. JIS A 1406 and ASTM D6245-12 refer personal carbon dioxide production rate. However JIS does not take into account personal attribute like as body height and weight. On the other hand, ASTM does not take into account gender difference and based on average westerner adult data. Hence, by using Douglas bag method with approximately total 70 voluntary Japanese subjects, a prediction equation for occupants’ carbon dioxide production rate included in exhaled breath is developed. Moreover, the equation is tested in single zone with occupants aiming at accuracy testing. The results can allow predicting more correct carbon dioxide concentration produced by occupants’, exhaled breath in single zone compared with the standards.