f-factor (conversion factor) f-factor (conversion factor) in diagnostic radiology, the f-factor is the conversion factor between exposure to ionizing radiation and the absorbed dose from that radiation. in other words, it converts between the amount of ionization in air (roentgens or, in si units, coulombs per kilogram of absorber material) and the absorbed dose in air (rads or grays). the two determinants of the f-factor are the effective atomic number (z) of the material and the type of ionizing radiation being considered. since the effective z of air and soft tissue is approximately the same, the f-factor is approximately 1 for many x-ray imaging applications. however, bone has an f-factor of up to 4, due to its higher effective z. radiation-related quantities the following table shows radiation quantities in si and non-si units. ionizing radiation related quantities quantity unit symbol derivation year si equivalent activity (a) becquerel bq s−1 1974 si unit curie ci 3.7 × 1010 s−1 1953 3.7×1010 bq rutherford rd 106 s−1 1946 1,000,000 bq exposure (x) coulomb per kilogram c/kg c⋅kg−1 of air 1974 si unit röntgen r esu / 0.001293 g of air 1928 2.58 × 10−4 c/kg absorbed dose (d) gray gy j⋅kg−1 1974 si unit erg per gram erg/g erg⋅g−1 1950 1.0 × 10−4 gy rad rad 100 erg⋅g−1 1953 0.010 gy equivalent dose (h) sievert sv j⋅kg−1 × wr 1977 si unit röntgen equivalent man rem 100 erg⋅g−1 × wr 1971 0.010 sv effective dose (e) sievert sv j⋅kg−1 × wr × wt 1977 si unit röntgen equivalent man rem 100 erg⋅g−1 × wr × wt 1971 0.010 sv