The measure that is used to determine the loudness of a sound is:

The measure used to determine the loudness of a sound is the decibel. The decibel scale quantifies sound intensity in a way that aligns with human hearing; it reflects how we perceive changes in sound level. The human ear can detect a wide range of sound intensities, and the decibel scale is logarithmic, meaning that an increase of 10 decibels represents a tenfold increase in intensity, which corresponds to a perceived doubling of loudness.

Hertz, on the other hand, measures frequency and indicates how many cycles per second a sound wave produces, rather than its loudness. While frequency can affect the perception of sound quality and pitch, it does not measure how loud that sound is.

Amplitude relates to the height of the sound wave, which impacts loudness indirectly; however, it is not the direct measurement used to assess how loud a sound is perceived. Thus, while amplitude does play a role in determining loudness, the standardized measure that best reflects human perception is the decibel.

In summary, decibels provide a clear and effective measure of sound loudness, making it the appropriate choice for this question.