What physical measurement expresses pitch?

The measurement that expresses pitch is Hertz (Hz). Pitch is the perception of how high or low a sound is, and it is directly related to the frequency of sound waves. When we talk about frequency, we refer to the number of cycles of a sound wave that occur in one second, which is measured in Hertz. The higher the frequency (more cycles per second), the higher the perceived pitch, and conversely, the lower the frequency, the lower the perceived pitch.

Decibels (dB) measure the intensity or loudness of a sound but do not relate to its pitch. Pascals (Pa) are a unit of pressure and are sometimes used in acoustics to express sound pressure levels but do not describe pitch either. Octaves are intervals between pitches where one frequency is double or half of another, but they are not a direct measurement of pitch—the term is more about musical intervals rather than the rate of oscillation that defines pitch. Thus, Hertz is the most accurate representation of pitch measurement in terms of frequency.