Radiation dose is measured in sieverts (Sv). Mostly, in dealing with natural and background radiation, we talk in thousandths of sieverts -millisieverts (mSv) or in millionths - microsieverts (µSv).
Some examples of doses are:
12 mSv whole body CT scan
0.13 mSv mammogram
0.08 mSv chest x-ray
5 µSv/h aeroplane flying at an altitude of 12 kilometres