Hearing Threshold Level dB HL = SPL – Reference SPL

dB HL = SPL (dB) – Reference SPL
Select what to solve for — enter the other two values,then click Check
Solve for:
Frequency: Ref SPL:7.0 dB
dB HL
dB SPL
dB
Hearing Level —
Normal (<25) Mild (25–40) Moderate (41–55) Severe (>55)
Reference SPL values (ANSI S3.6-2010) · Normal hearing:≤25 dB HL
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Hearing Threshold Level Conversion

Converts a raw sound pressure level measurement into clinically standardized hearing-level decibels used on audiograms.

Written by the Vorzep Team

BiomedicalClinicalAudiology

Hearing Threshold Level CalculatordB HL = SPL – Reference SPL

dB HL = SPL (dB) – Reference SPL
Select what to solve for — enter the other two values, then click Check
Solve for:
Frequency:Ref SPL: 7.0 dB
dB HL
dB SPL
dB
Hearing Level—
Normal (<25) Mild (25–40) Moderate (41–55) Severe (>55)
Reference SPL values (ANSI S3.6-2010) · Normal hearing: ≤25 dB HL
dB HL = SPL(dB) - Reference SPL at that frequency
Hearing Threshold Level Conversion

Variables

SymbolQuantityUnit
dB HLHearing leveldB HL
SPLMeasured sound pressure leveldB SPL
Reference SPLFrequency-specific reference SPLdB SPL

What it means

The hearing threshold level (dB HL) is the standard unit used in audiometry to express hearing sensitivity relative to a normative reference. The reference SPL (sound pressure level) varies with frequency, as the human ear has different sensitivity (e.g., reference SPL is lower at 1000 Hz than at 125 Hz). The conversion subtracts the reference SPL from the measured SPL. This standardises audiometric results so that 0 dB HL represents the average normal hearing threshold. The formula is used to plot audiograms and to diagnose hearing loss. Understanding this conversion is essential for audiologists to interpret test results and to fit hearing aids. It also ensures consistency across different audiometers.

Worked example

Hearing Threshold Level – Two Examples

Real‑World
Scenario: SPL = 30 dB, reference SPL = 7.5 dB. Find dB HL.
ParameterValue
SPL30 dB
Reference SPL7.5 dB
1dB HL = 30 - 7.5 = 22.5 dB HL
Result 22.5 dB HL ✓ Normal
Scenario: SPL = 45 dB, reference = 9.5 dB. Find dB HL.
ParameterValue
SPL45 dB
Reference9.5 dB
1dB HL = 45 - 9.5 = 35.5 dB HL
Result 35.5 dB HL ✓ Mild loss
Clinical insight: dB HL normalises hearing thresholds across frequencies (0–20 dB HL = normal hearing).

Common mistakes

  • Reference SPL: The sound pressure level corresponding to 0 dB HL at each frequency (e.g., 250 Hz: 24 dB SPL, 500 Hz: 11 dB SPL, etc.). Use the correct ANSI reference values.
  • Units: Both SPL and reference are in dB SPL – the result is in dB HL.
  • Frequency‑specific: The conversion depends on frequency – do not use a single offset.
  • Calibration: Audiometers are calibrated to dB HL; this formula is for converting measurements from sound level meters.

Applications

Hearing threshold level (dB HL) is obtained by subtracting the reference sound pressure level (SPL) for each frequency from the measured SPL. This conversion standardises audiometric measurements, allowing comparison of hearing thresholds across individuals and across test equipment. Audiologists and otolaryngologists use dB HL to diagnose hearing loss, to fit hearing aids, and to monitor changes in hearing over time. The reference SPL values are derived from normative data for each frequency. By understanding this conversion, clinicians can accurately interpret audiograms and provide appropriate interventions, including hearing aids, cochlear implants, and tinnitus management.

  • Interpretation of pure‑tone audiometry results
  • Diagnosis and classification of hearing loss
  • Selection and programming of hearing aids
  • Monitoring of auditory function in noise‑exposed individuals
  • Research on auditory physiology and pathology