Hearing deficit is classified according to quantitative (the audiometric assessment provides the degree of deafness), qualitative or topodiagnostic (defining the seat of damage) and chronological criteria. The latter refer to the period in which the damage arose.

According to the BIAP (Bureau International d'Audiophonologie) the average total hearing loss is calculated considering the frequencies 500, 1000, 2000, 4000 Hz, And the sum of hearing loss in dB of the frequencies considered is divided by four in order to calculate the average loss.

According to these criteria, the following are considered:

• Normal hearing (auditory threshold below 20 dB).
• Mild deafness (auditory threshold between 20 and 40 dB).
• Medium deafness (threshold between 40 and 70 dB).
• Serious deafness (auditory threshold between 70 and 90 dB).
• Total deafness between 90 and 120 dB.
• Total hearing loss above 120 dB.

According to the seat of the lesion, hypoacusis is divided into:

• Transmissive or by conduction
• Neurosensory or perceptive
• Mixed