One one-thousandth (1/1000) of a rad. To change a rad, divide by 1,000. A dental X-ray gives a thyroid dose of about 3 millirad. The Hanford IDA Project is providing thyroid dose estimates in millirad.

A unit of measuring radiation dose equal to one thousandth of a RAD.

It is 1/1000th of a rad. Rad stands for radiation absorbed dose and is defined as the dosage of radiation that deposits 1x10-2 J of energy per kilogram of tissue. However, in biological systems the effect of radiation depends on the type of radiation, e.g., alpha, beta or gamma radiation.