Which wave property is measured in hertz?

The wave property measured in hertz is frequency.

Frequency is the number of complete cycles or repetitions a wave makes per unit of time. The hertz, abbreviated Hz, is the SI unit of frequency: one hertz means one cycle per second. A wave oscillating 1,000 times per second has a frequency of 1,000 Hz, or 1 kilohertz.

Frequency is closely related to period, the time required for one cycle. They are reciprocals: increasing the frequency shortens the period. For a wave traveling at a fixed speed, frequency and wavelength are also linked by v = fλ. When a wave enters another medium, its frequency generally remains fixed while its speed and wavelength change.

In sound, frequency strongly influences perceived pitch, while amplitude is associated more closely with loudness. Intensity describes energy flow, and polarization describes the orientation of oscillations in suitable waves. These properties can all matter in wave science, but they are not what the unit hertz measures.

The unit is named for German physicist Heinrich Hertz, whose experiments in the late nineteenth century provided convincing evidence for electromagnetic waves. The name became an official SI unit in 1960, replacing “cycles per second.”