Abstract: A formula is presented in this paper for the relative annual damaging ultraviolet radiation (DUV) dose at different tropical and mid-latitude sites. The “DUV dose” signifies the solar energy incident on a horizontal surface, weighted by the erythemal response spectrum (Robertson 1975, Scotto et al. 1976, Cutchis 1974). The DUV dose is assumed equivalent to the “dose” which would be measured by a Robertson-Berger meter unit (Robertson 1975, Scotto et al. 1976). The DUV formula consists of six multiplicative factors which include the effects of amount of ozone, latitude, altitude, cloudiness, ground albedo, and amount of aerosols. A seasonal ozone variation factor is introduced to modify the tropical relative DUV formula for application to mid-latitude sites. The formula has been developed by mathematically fitting sometimes sparse data, and remains to be validated in the general sense.