Radiation Units of Measurement | Roentgen,Gray (Gy), Rad, REM

This page mentions Radiation Units of Measurement. It describes basics and conversions between Roentgen, Gray (Gy), Rad and REM used as Radiation Units of Measurement.


• It is measurement of energy produced by gamma and x-ray radiations in one cubic centimeter of air.
• It is abbreviated as capital letter "R".
• One milliroentgen (i.e. "mR") is equal to (1/1000) of one roentgen.
• One microroentgen (i.e. "µR") is equal to (1/106) of on roentgen.

Gray (Gy)

• The System International units for radiation measurements are "gray" (abbreviated as "Gy") and "sivert" (abbreviated as "Sv" ) for absorbed dose & equivalent dose respectively.


• It is abbreviation of "Radiation Absorbed Dose".
• It is measurement unit used for absorption of all types of ionizing radiation viz. alpha, gamma, beta, neutrons into any medium.
• One RAD is equivalent to absorption of 100 ergs of energy per gram of absorbing tissue.


• It is abbreviation of "Roentgen Equivalent Man".
• It is measurement which correlates dose of any radiation to biological effect of the same radiation.
• All the radiations will have different biological effects and hence dosage is multiplied by quality factor "Q".
• Alpha particles will cause three times more damage compare to gamma rays. Hence alpha radiation has "Q" of 3.

Difference between rad and rem is as follows.
➤RAD is measurement of radiation absorbed by material or tissue.
➤REM is measurement of biological effect of the absorbed radiation.

Conversion between Radiation Units of Measurement

Conversions between one unit and the other are as follows.
➤1 Sv = 100 REM
➤1 mSv = 100 mR (mrem)
➤1Gy (i.e. Gray) = 100 RAD
➤1 mGy = 100 mRAD

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