Rad (rad)

The rad (symbol: rad) is a legacy unit of absorbed radiation dose defined as the energy deposition of 100 ergs per gram of matter, equal to exactly 0.01 grays or 0.01 joules per kilogram. Formally defined in 1953 by the International Commission on Radiation Units and Measurements (ICRU), the rad was the standard clinical unit for decades until the General Conference on Weights and Measures officially replaced it with the SI gray in 1975.