Noise, installation and procurement

Octave Band to dBA Calculator

Combine compatible unweighted octave sound-pressure bands to estimate dBA and each band’s energy contribution.

Calculation inputs

This calculator runs in your browser and requires JavaScript.

An example is loaded automatically. Replace it with your project values; the result updates as you edit.

Included octave-band centers Choose exactly the complete supplied range. Results always identify their included band centers; missing frequency ranges are not inferred.

Receiver, time and unweighted spectrum reference Identify receiver, operating state, source/model, unweighted pressure reference and common averaging interval. Measured bands should be simultaneous Leq over the same interval; independently timed maxima or already weighted levels are not interchangeable.

Worked-example data and reference

Oeler published nine-band numeric example, treated here as a compatible modeled receiver spectrum for arithmetic only. Actual field receiver/time records are not verified. Replace with a complete unweighted 31.5–8000 Hz spectrum on a matched receiver/time or modeled mean-square basis.

These example values are for the worked calculation. Replace them with the source and conditions for your own case.

Spectrum and time-basis confirmation Confirm a complete unweighted receiver sound-pressure spectrum re 20 µPa for the chosen range, on a common mean-square/time basis. This center-correction estimate does not accept sound power, overall dBA or independently timed maxima.

31.5 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

63 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

125 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

250 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

500 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

1000 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

2000 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

4000 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

8000 Hz unweighted band level (dB re 20 µPa) Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.

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Result

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Results appear automatically when inputs are valid.

Formula and source basis

Concepts behind this calculation

Estimate A-weighted and unweighted levels from complete unweighted octave-band receiver sound pressure, with explicit frequency coverage and a per-band correction and energy table.

An octave-band estimate of A-weighted sound pressure starts by applying the center-frequency correction to each unweighted receiver band. The corrected levels are converted to relative mean-square energies and summed before converting back to decibels. Adding decibel numbers directly would not preserve acoustic energy. The unweighted total uses the same bands without the A corrections, providing a useful comparison of spectral weighting.

Both totals cover only the selected frequency range and common time basis. Independently timed maxima need not occur together and cannot automatically form one valid combined level. Center corrections also approximate the energy distribution within each octave; strong narrowband content can differ from an actual A-filter measurement. A missing band is unknown energy, while a numeric zero-decibel entry represents finite energy.

How to use this calculator

Select Included octave-band centers to match the complete supplied spectrum.
Complete Receiver, time and unweighted spectrum reference and establish Spectrum and time-basis confirmation.
Enter every selected unweighted band level at the same receiver and common interval. Compare both totals and the per-band corrections and weighted-energy percentages while retaining the stated frequency coverage.

Calculation method and applicability

L_A,bands = 10 log10[Σ10^((Li+Ai)/10)]; L_unweighted,bands = 10 log10[Σ10^(Li/10)]. Weighted energy share_i = 100 × 10^((Li+Ai)/10) / Σ10^((Lj+Aj)/10). Ai is the tabulated center-frequency A correction. An overall dB number alone is not enough to perform this conversion.

Li = unweighted band sound pressure level (dB re 20 µPa); Ai = center-frequency A correction (dB). LA,bands is the A-weighted energy sum for the entered frequency range; energy shares are percent.

Input definitions and units

Included octave-band centers: Choose exactly the complete supplied range. Results always identify their included band centers; missing frequency ranges are not inferred. Choices: 31.5–8000 Hz · nine bands; 63–8000 Hz · eight bands; 31.5–16000 Hz · ten bands.
Receiver, time and unweighted spectrum reference: Identify receiver, operating state, source/model, unweighted pressure reference and common averaging interval. Measured bands should be simultaneous Leq over the same interval; independently timed maxima or already weighted levels are not interchangeable.
Spectrum and time-basis confirmation: Confirm a complete unweighted receiver sound-pressure spectrum re 20 µPa for the chosen range, on a common mean-square/time basis. This center-correction estimate does not accept sound power, overall dBA or independently timed maxima. Choices: Not established; Unweighted receiver bands and common basis established.
31.5 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero. Applies to Included octave-band centers: 31.5–8000 Hz · nine bands or 31.5–16000 Hz · ten bands.
63 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
125 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
250 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
500 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
1000 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
2000 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
4000 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
8000 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero.
16000 Hz unweighted band level (dB re 20 µPa): Enter the unweighted octave-band pressure level on the common receiver/time basis. Negative dB levels and 0 dB represent finite energy. Do not replace a missing band with zero. Applies to Included octave-band centers: 31.5–16000 Hz · ten bands.

How to interpret the result

Report the A-weighted estimate with its included band centers and common measurement or model basis. Energy shares identify contributors within that coverage; they do not describe omitted frequencies, sound quality or an exposure assessment.

Worked examples

31.5–8000 Hz · nine bands

Inputs: Oeler published numeric example at 31.5–8000 Hz: 14.5, 41, 48, 44.9, 46.8, 44.1, 39.5, 33.4 and 19.1 dB unweighted receiver bands. Treat these as a compatible modeled spectrum for this arithmetic example.

Calculation: Apply corrections of −39.4, −26.2, −16.1, −8.6, −3.2, 0, +1.2, +1.0 and −1.1 dB. Sum the corrected mean-square energies and take 10 log10. Sum the original energies separately for the unweighted result.

Result: 48.390 dB(A) estimated from the entered 31.5–8000 Hz bands; unweighted total 52.819 dB. These round to the peer display of 48.4 and 52.8 dB.

63–8000 Hz · eight bands

Inputs: Oeler example subset at 63–8000 Hz: 41, 48, 44.9, 46.8, 44.1, 39.5, 33.4 and 19.1 dB. The 31.5 Hz band is omitted, rather than treated as 0 dB.

Calculation: Use only the eight selected octave-band corrections and sum energies separately for weighted and unweighted values.

Result: 48.390 dB(A) estimated from 63–8000 Hz bands; unweighted total 52.818 dB. Its similarity to nine bands follows from this example’s low 31.5 Hz energy and is not a general equivalence.

31.5–16000 Hz · ten bands

Inputs: Cirrus published 31.5–16000 Hz spectrum: 70.9, 78.4, 83.3, 87.6, 87.3, 93.5, 93.8, 97, 99.9 and 98.2 dB, with a common Leq basis stated by the author.

Calculation: Apply the nine lower-band corrections and −6.6 dB at 16 kHz, then sum weighted energies. The independent unrounded result is 103.239463257 dB(A).

Result: 103.239 dB(A) estimated from 31.5–16000 Hz bands, rounding to the source’s 103.2 dB(A). Agreement for this example does not guarantee agreement with a full-band meter for every spectrum.

Assumptions and limits

Uses tabulated center-frequency A corrections as an octave-band approximation. Strong narrowband tones or unusual energy distributions inside a band can differ from an actual A-filter result. No within-band spectrum is inferred.
Results include only the chosen octave-band range. Frequencies outside that range are omitted, not entered as zero or reconstructed; their contribution can make a full-band meter result different. The 31.5–16000 Hz profile still does not guarantee full-band equivalence.
Measured band Leq values must describe the same receiver, operating state and common interval. Independently timed maxima, instantaneous/time-weighted meter readings and inconsistent modeled spectra are not automatically additive. The reference field is user-supplied and not authenticated.
Only unweighted sound-pressure levels re 20 µPa are accepted. Sound power re 1 pW, already frequency-weighted bands, and an overall dBA value cannot be substituted or uniquely inverted to obtain a spectrum. No room/source transfer is modeled.
No NC/RC/NR rating, subjective loudness, tonality/low-frequency quality, hearing-exposure dose, instrument tolerance, current standard conformity or project/code pass/fail is calculated. The input bounds of −100 to 200 dB provide numeric support; they do not establish an instrument dynamic range or valid physical measurement.

FAQs

Why can a strong low-frequency band contribute little to the weighted total?

Its A correction may substantially reduce its weighted level. The weighted-energy share shows its contribution after that correction, so a band dominant in the unweighted spectrum need not dominate the A-weighted estimate.

Can I recover octave bands from an overall dBA reading?

No unique spectrum follows from one total. Many different band distributions produce the same dBA, so this calculation requires the actual unweighted receiver bands over the chosen range.

Sources

ASHRAE 2021 Fundamentals, Chapter 8: Sound and Vibration, Tables 5–6Table 5 provides center-frequency A corrections through 8 kHz for the bands used here. The combining-levels section and Table 6 describe energy addition and correcting each band before aggregation. Full current standard or sound-meter conformity is not inferred.
Cirrus Research: Calculation of dBA from Octave Band Sound Pressure Levels, March 19, 2020The instrument manufacturer explains common Leq timing and limited frequency coverage. Its 31.5–16 kHz table includes the −6.6 dB correction at 16 kHz, with a worked result of 103.2 dB(A). This example does not guarantee agreement for every spectrum.
Oeler Industries: dBA CalculationNine-band calculator comparison. Its lowest band is labeled 31 Hz; this tool uses the primary tables’ nominal 31.5 Hz correction. The published 48.4/52.8 dB result and an executed flat-40 dB case of 47.0/49.5 dB agree after rounding. This is not a field measurement or formula authority.

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