The dose of one rad indicates the absorption of 100 ergs (an erg is a small but measurable amount of energy) per gram of absorbing material.

One roentgen of gamma radiation exposure results in approximately one rad of absorbed dose.

To indicate the dose an individual receives in the unit rad, the word "rad" follows immediately after the magnitude, for example, "50 rad." One thousandth of a rad is abbreviated "mrad" or "millirad."