Grades of hearing impairment
| Grade of impairment | Corresponding audiometric ISO value | Performance | Recommendations |
| 0 - No impairment | 25 dB or better (better ear) |
No or very slight hearing problems. Able to hear whispers. | |
| 1 - Slight impairment | 26-40 dB (better ear) |
Able to hear and repeat words spoken in normal voice at 1 metre. | Counselling. Hearing aids may be needed. |
| 2 - Moderate impairment | 41-60 dB (better ear) |
Able to hear and repeat words spoken in raised voice at 1 metre. | Hearing aids usually recommended. |
| 3 - Severe impairment | 61-80 dB (better ear) |
Able to hear some words when shouted into better ear. | Hearing aids needed. If no hearing aids available, lip-reading and signing should be taught. |
| 4 - Profound impairment including deafness | 81 dB or greater (better ear) |
Unable to hear and understand even a shouted voice. | Hearing aids may help understanding words. Additional rehabilitation needed. Lip-reading and sometimes signing essential. |
Grades 2, 3 and 4 are classified as disabling hearing impairment.
The audiometric ISO values are averages of values at 500, 1000, 2000, 4000 Hz.