Last revised by Bahman Rasuli on 12 Dec 2020

The hertz (Hz) is the derived SI unit for frequency. One hertz represents one cycle per second, and thus in base SI units, equates to one per second (1/s). In radiology, it is usually encountered in the context of ultrasound physics.


As for all other eponymous units when the name is written out in full it is not capitalized, but its symbol is capitalized. Hertz is also the plural form; "hertzs" is incorrect.

History and etymology

The unit is named after Heinrich Rudolf Hertz (1857-1894) 2, a brilliant German physicist, remembered chiefly for his achievement in proving the existence of electromagnetic waves 1,2. Interestingly, in retrospect, it is now the historical consensus that he suffered from granulomatosis with polyangiitis (Wegener granulomatosis), which explains his premature death at the age of only 36 years old 2.

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