RNID: For deaf and hard of hearing people.

Measuring hearing loss and deafness

We usually measure hearing loss and deafness by finding the quietest sounds someone can hear using tones with different frequencies, which are heard as different pitches. The tester asks the person being tested to respond - usually by pressing a button - when they can hear a tone, and the level of the tone is adjusted until they can just hear it. This level is called the threshold.

Thresholds are measured in units called dBHL, where dB stands for decibels and HL stands for hearing level. We consider anyone with thresholds between 0 and 20dBHL across all the frequencies to have "normal" hearing. The greater someone's threshold level is in dBHL, the worse their hearing loss.

Definitions of deafness

  • People with mild deafness have some difficulty following speech, mainly in noisy situations. The quietest sounds they can hear in their better ear average between 25 and 39 decibels.
  • People with moderate deafness have difficulty in following speech without a hearing aid. The quietest sounds they can hear in their better ear average between 40 and 69 decibels.
  • People with severe deafness rely a lot on lipreading, even with a hearing aid. British Sign Language (BSL) may be their first or preferred language. The quietest sounds they can hear in their better ear average between 70 and 94 decibels.
  • People who are profoundly deaf communicate by lipreading. BSL may be their first or preferred language. The quietest sounds they can hear in their better ear average 95 decibels or more.

Deaf and hard of hearing people in Northern Ireland

This table shows the estimated numbers of deaf and hard of hearing people in Northern Ireland.

Estimated number of deaf and hard of hearing people in Northern Ireland, broken down by age group.
 Level of deafness 16 to 60 years oldOver 60 years old  Total
Mild/moderate deafness62,000 140,000 202,000 
Severe/profound deafness 3,00014,000 17,000 
All degrees of deafness 65,000 154,000 219,000 

Further information

Our factsheet "Facts and figures on deafness and tinnitus" has more statistics and guidance on how to use them.