How to Read an Audiogram — Calculating Hearing Level and Japan’s Disability-Certificate Grades

1. How the exams ask about it

Each chapter carries a coloured tag showing which exam it relates to: Certified interpreter exam marks the rounds where it was asked, Unified exam marks items in the training curriculum.

2. The axes, the circles ○ and the crosses ×

The horizontal axis is frequency, in hertz (Hz). The left is low pitch and the right is high pitch. The recording sheet runs 125, 250, 500, 1000, 2000, 4000 and 8000 Hz, so the frequency doubles at every step.

The vertical axis is hearing level, in decibels (dB). The hearing-conservation manual of the Japan Society of Otorhinolaryngology–Head and Neck Surgery explains that the softest sound a person can “just barely hear” is expressed as its difference from the threshold of a normal ear, which is why it is called the hearing level and why it shows the degree of hearing loss. So 0 dB does not mean “no sound”; it is the position of normal hearing. The further down a mark sits, the louder a sound has to be before it is heard.

On symbols, the same manual says the right ear is shown with ○ and the left ear with ×. Most sheets draw the right ear in red (○) and the left in blue (×). Joining the points with a solid line for the right ear and a dashed line for the left gives a line graph of hearing. If a frequency is not heard even at the loudest output, a downward arrow is added to the symbol.

Figure 1 is an invented example. In both ears, low pitches are heard at 20–35 dB and the line falls toward the high pitches. For a downward slope like this, the manual notes that age-related decline “starts in the high-frequency range.” A dip around 4000 Hz alone (the c5 dip) is described as a characteristic early sign of noise-induced hearing loss.

3. Air conduction and bone conduction

First, the parts of the ear. The outer ear (the auricle and the ear canal) and the middle ear carry sound vibration to the inner ear. The inner ear and beyond pick up that vibration and pass it to the nerve.

The middle ear holds the ossicles. From the eardrum inward, the malleus, incus and stapes form a chain that carries the eardrum’s vibration through the stapes into the inner ear (“Middle ear,” Heibonsha World Encyclopedia, revised edition, via Kotobank, in Japanese).

The circles and crosses in Figure 1 are air-conduction results, measured by listening through headphones. There is a second test, bone conduction, in which a vibrator placed on the bone behind the ear sends sound straight to the inner ear. Bone conduction is marked on the same chart with [ for the right ear and ] for the left. The bracket direction shows the side, so Figures 3 and 4 leave the bone-conduction marks uncoloured.

The gap between air and bone conduction (the air–bone gap) is what tells conductive hearing loss apart from sensorineural hearing loss (Sano, “Pure-tone audiometry in practice,” Audiology Japan 67(2), 2024).

Here are two examples, right ear only.

There is also loss where both drop and air conduction drops further still. Air conduction alone cannot tell you which type you are looking at.

With sensorineural loss, making a sound louder does not always make speech clear. The Japan Audiological Society’s classification includes a line in its description of severe loss to the effect that even when sound is heard, there is a limit to how much is understood. The disability-certificate table below has a separate criterion based on speech discrimination, apart from decibels, and I read that as a way of capturing this side of hearing.

4. Four formulas for the average

An audiogram has around seven values, one per frequency. To say “the right ear’s hearing is so many dB” you take an average, and this is where the formulas part ways. In the formulas, “500”, “1000” and so on stand for the hearing level (dB) at that frequency.

The Japan Audiological Society recommends average B and also accepts the 3-frequency average and average A. The 6-weight formula is the one used to grade hearing loss under workers’ compensation insurance (Labour Standards Bureau notice No. 565, 30 September 1975). The disability-pension criteria also use it as a reference when the value from average A is close to a grade boundary. The certified interpreter exam has also asked about the formula used under workers’ compensation insurance.

Average A counts 1000 Hz twice. Average B brings in 4000 Hz. For an ear that loses the high pitches first, a formula that includes 4000 Hz comes out larger.

Take the right ear in Figure 1: 30 dB at 500 Hz, 40 dB at 1000 Hz, 60 dB at 2000 Hz, 75 dB at 4000 Hz.

• Avg A30 + 40×2 + 604= 42.5 dB
• Avg B30 + 40 + 60 + 754= 51.3 dB
• 3-freq.30 + 40 + 603= 43.3 dB
• 6-weight30 + 40×2 + 60×2 + 756= 50.8 dB

The same ear differs by almost 9 dB between average A and average B. The left ear is 47.5 dB on average A and 56.3 dB on average B.

The certificate has further rules. Under Japan’s certification criteria, hearing is measured with hearing aids removed, any frequency at which 100 dB cannot be heard is entered as 105 dB, and if several tests were done within a short period, the best result is used.

5. The Japan Audiological Society’s degrees

In July 2014 the Society’s committee on hearing loss published a report on how to classify the degree of hearing loss. It recommends average B.

The report says the classification is not a diagnostic one but was made from the standpoint of assessing the everyday difficulties hearing loss causes. It also says that the same degree of loss can mean a different level of disability depending on the nature of the loss and the person.

6. The WHO grades

The WHO set out its grades of hearing loss in the World report on hearing (March 2021). It uses the same frequencies as average B — 500, 1000, 2000 and 4000 Hz — and grades on the better ear.

Compared with the Japan Audiological Society, the upper limit of normal is 20 dB rather than 25 dB, and the bands are narrower. The WHO fact sheet defines hearing loss greater than 35 dB in the better ear as “disabling hearing loss.”

7. Japan’s disability-certificate grades

Grades on Japan’s physical disability certificate are set by Appended Table 5 of the Enforcement Regulations of the Act on Welfare of Physically Disabled Persons. The hearing section reads as follows (my translation).

Points worth noting:

• There is no grade 1 or grade 5 for hearing.
• Grade 2 says 100 dB or more in each ear, not as an average of the two.
• Grade 6 (2) applies when one ear is 90 dB or more and the other is 50 dB or more.
• Grade 4 (2) is decided by speech discrimination, not decibels. Single-syllable test words are presented at a normal speaking level and the percentage correctly heard is calculated (certification criteria).
• When grade 2 is newly diagnosed for someone who does not hold a certificate, an objective test such as the auditory brainstem response (ABR) must be done and its record attached (certification guidelines, as handled from April 2015).

8. The yardsticks side by side

Adding the Deaflympics to the standards above gives four yardsticks. The International Committee of Sports for the Deaf (ICSD), which runs the Deaflympics, requires a better-ear average of at least 55 dB over 500, 1000 and 2000 Hz (3-frequency, air conduction).

Applying them to the example hearing in Figure 1:

• Japan Audiological Society: right 51.3 dB, left 56.3 dB — both moderate
• WHO: the better (right) ear at 51.3 dB — moderately severe
• Disability certificate: right 42.5 dB, left 47.5 dB — short of the hearing-level threshold (70 dB in both ears)
• Deaflympics: the better (right) ear at 43.3 dB — short of 55 dB

The example hearing in Figure 1 is moderate by the Society’s scheme, yet short of the certificate’s hearing-level threshold. Moderate loss is 40 to under 70 dB. The certificate’s hearing-level criteria start at 70 dB in both ears, so if both ears are in the moderate range, the hearing-level criteria do not make someone eligible for the certificate. The certificate also has the speech-discrimination route to grade 4, though, so hearing level alone does not settle whether someone qualifies.

Organisations of hard-of-hearing people have called for this line to be reconsidered. The resolution of the 21st National Welfare Convention of Late-Deafened and Hard-of-Hearing People (November 2015) set out a “decibel-down campaign,” citing an “international standard (average of 41 dB or more in both ears over 500 Hz–4 kHz)” and stating that “Japan’s standard for disability (average of 70 dB or more in both ears over 500 Hz–2 kHz) is detached from the realities of life for people with hearing loss” (my translation).

9. Numbers to check before the exam

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A study app focused on the written exam (basic knowledge and Japanese language) of the National Unified Examination for Sign-Language Interpreters. I spent 12 years teaching at a special-needs school for the Deaf, and wrote the practice questions to follow the scope the exam publishes. Hearing-level calculations and certificate grades from this article are among the basic-knowledge questions.

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Closing

An audiogram records the hearing level at which pure tones begin to be heard. How well speech is understood, how things go in a noisy room, how easy conversation is — the chart alone does not decide any of that. The Japan Audiological Society’s report also says that the same degree of loss can mean a different level of disability from person to person.

To experience a simulation of hearing loss, try these learning tools on our site (in Japanese).

The way I have organised this is one way of looking at it. How tests are done and how results are written can differ by clinic and region. If you were taught differently, or you think a piece of this is off, I would be glad to hear it through the contact form (the article name is filled in for you).