Noise exposure is a basic concept used to assess the risk of noise induced hearing loss in the workplace. It is very important, since loud noise is omnipresent in almost all human activity, especially in industry, construction, mining and transportation. The question to answer is how to determine the risk of a person performing in an environment where the noise levels, duration and frequency content change with time. The answer is obtained by measuring his noise exposure. Although the measurement itself is not complex or difficult, a proper knowledge of what exactly is the noise exposure and how to deal with the measurement result in fundamental to avoid getting wrong conclusions.