A-weighting is a standardized frequency-response curve (IEC 61672-1) applied to sound measurements to approximate how the human ear perceives loudness. The ear is most sensitive around 3–4 kHz and progressively less sensitive at low and very high frequencies. A-weighting boosts mid-range frequencies and attenuates lows and highs accordingly, producing a single-number level in dB(A).

What is the formula for A-weighting?

The IEC 61672 formula defines A(f) = 2 + 20 × log₁₀[ f⁴ × 12200² / ((f² + 20.6²)(f² + 12200²)√((f² + 107.7²)(f² + 737.9²))) ]. This fourth-order rational function produces corrections ranging from about −70 dB at 10 Hz to +1.2 dB near 3–4 kHz and back down at 20 kHz.

When should I use dB(A) vs. dB(C)?

Use dB(A) for most occupational-noise and environmental-noise regulations — it best models steady-state perceived loudness for typical noise sources. Use dB(C) (flat above 30 Hz) when measuring impulsive sounds like gunshots, or when assessing low-frequency sources such as subwoofers or explosions, where A-weighting would unfairly discount the energy.

Why does A-weighting give negative corrections at low frequencies?

The human ear becomes progressively less sensitive below about 500 Hz. A-weighting subtracts decibels at low frequencies to reflect that. At 63 Hz the correction is about −26 dB, meaning a 70 dB pure tone at 63 Hz sounds roughly as loud as a 44 dB(A) tone at 1 kHz.

Can I use this calculator for broadband noise?

This tool is designed for single-frequency (tonal) analysis or for computing per-band corrections in an octave-band or 1/3-octave-band analysis. For broadband noise, compute the A-weighted level in each band and then combine them logarithmically: L_A_total = 10 × log₁₀(Σ 10^(L_A_band/10)).

A-Weighting Calculator

Enter a frequency and unweighted sound level (dB) to get the A-weighted result in dB(A).

Input

Frequency (Hz)

Range: 10 – 20,000 Hz

Sound Pressure Level (dB)

Unweighted SPL at the given frequency.

Result

A-Weighting at Octave Centers

Correction values per IEC 61672-1.

Freq (Hz)	A(f) dB

Summary

A-weighting is a frequency-dependent correction applied to sound pressure levels to approximate the human ear's sensitivity, which varies strongly with frequency. The A-weighted level in dB(A) equals the unweighted dB plus the A-weighting correction factor at that frequency, as defined by IEC 61672-1. This calculator computes the exact A(f) correction from the standard fourth-order rational formula and applies it to your input level.

How it works

Enter the frequency of the sound in hertz (Hz), from 10 Hz to 20,000 Hz.
Enter the unweighted sound pressure level in decibels (dB).
The calculator applies the IEC 61672 A-weighting formula to find the correction A(f) at that frequency.
The A-weighted level is calculated as: L_A = L_dB + A(f).
Results update instantly; adjust either input to compare different tones.
The table below shows A-weighting corrections at standard octave-band center frequencies for reference.

Use cases

Convert a single-frequency noise measurement from dB to dB(A) for regulatory compliance.
Understand why low-frequency machinery noise (100 Hz) is penalized less than mid-frequency HVAC tones (1 kHz) under A-weighting.
Verify hand calculations when computing A-weighted octave-band levels before summing them.
Compare the perceived loudness of different pure tones by checking their A-weighted levels.
Educate students on the IEC 61672 A-weighting curve and its mathematical basis.
Quickly look up the A-weighting correction at any non-standard frequency not covered by tabulated data.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu