What measurement is used to express the faintest sound detectable by humans?

The faintest sound detectable by humans is measured in decibels. Decibels are a logarithmic unit that quantifies sound intensity relative to a reference level, making it an effective way to express the perception of sound, as human hearing sensitivity can vary greatly across different frequencies. The threshold of hearing, typically identified as 0 decibels, represents the faintest sound that the average human ear can detect in a quiet environment.

In contrast, the other units listed are not suitable for measuring sound perception directly. Watts/cm^4 and Watts/cm^2 are primarily used to describe power density and intensity in physics but do not effectively convey the subjective nature of sound perception. Dynes/cm^2 is a measurement related to force per unit area and is also not applicable to sound measurement. Thus, decibels are the standard unit used in audiology and acoustics to communicate sound levels effectively, including the faintest sound detectable by humans.