Roentgen is the common unit used to express the amount of gamma radiation exposure an individual receives.

In writing exposures, roentgen (pronounced rent-gen) is usually abbreviated with a capital "R," which follows immediately after the amount of gamma radiation received. An exposure of 50 roentgens would then be written "50 R." Milliroentgen is a subunit of the roentgen (one thousandth of a roentgen), and is abbreviated "mR."