The röntgen (roentgen) equivalent in man or rem (symbol rem) is a unit of radiation dose.


It is the product of the absorbed dose in röntgens (R) and the biological efficiency of the radiation.


More precisely, assuming a radiation weighting factor rW=1, 1 rem equals 1.07185 röntgen. The conversion factor has been readjusted from 1 to 1.07185 so that 100 rem equal 1 sievert;

SI derived unit[]

The sievert is the recommended SI derived unit, and in many cases is the legally prescribed unit.

Commonly used[]

A rem is a large amount of radiation, so the millirem (mrem), which is one thousandth of a rem, is often used for the dosages commonly encountered, such as the amount of radiation received from medical x-rays and background sources.

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