What unit of measurement is used to measure the frequency of electromagnetic waves?

The hertz is used to measure the frequency of electromagnetic waves. Different prefixes denoting subdivisions are used to aid measurement eg. kilohertz (1,000 cycles/sec), megahertz ( 1,000,000 cycles/sec), gigahertz (1,000,000,000 cycles/sec) and terahertz (1,000,000,000,000 cycles/sec).