Results of the audiometric evaluation are plotted on a chart called an audiogram. Loudness is plotted from top to bottom. Frequency is plotted from left to right. Hearing loss (HL) is measured in a scale of decibels normalized for human hearing (dB HL) and is described in general categories (below). 

The general hearing loss categories used by most hearing professionals are as follows:

Normal hearing (0 to 25 dB HL)
Mild hearing loss (26 to 40 dB HL)
Moderate hearing loss (41 to 70 dB HL)
Severe hearing loss (71 to 90 dB HL)
Profound hearing loss (greater than 91 dB HL)

Interestingly, some people may tell you they don't need hearing aids because they ONLY have a 30 decibel hearing loss. However when you plug your ears with your fingers, you'll experience approximately a 25 decibel hearing loss - and you'll quickly realize that going through your day with even a little hearing loss is quite irritating and disconcerting!

(by sicologic.com)