A-Weighting Correction Calculator
A-weighting adjusts a sound level measurement to reflect how the human ear responds to different frequencies, attenuating low bass and very high treble that we hear less strongly. The correction is defined precisely by the IEC 61672-1 standard with fixed pole frequencies and a normalization so that 1 kHz reads 0 dB. This calculator computes the exact A-weighting value in decibels at any frequency you enter, and applies it to an optional linear level to give the equivalent dB(A) reading. Use it to weight octave-band data, check a sound level meter, or understand why low-frequency noise reads lower in dB(A).
A-weighting formula (IEC 61672-1)
RA(f) = 12194.217^2 * f^4
/ ((f^2 + 20.598997^2)
* sqrt((f^2 + 107.65265^2)(f^2 + 737.86223^2))
* (f^2 + 12194.217^2))
A(f) = 20 * log10(RA(f)) + 2.00 dB
dB(A) = level + A(f)
The +2.00 dB term normalizes the curve to 0 dB at 1,000 Hz. The result is negative below about 1 kHz and slightly positive in the 2 to 4 kHz region.
Typical A-weighting values
- At 31.5 Hz the correction is about -39.4 dB; at 63 Hz about -26.2 dB.
- At 125 Hz about -16.1 dB; at 250 Hz about -8.6 dB; at 500 Hz about -3.2 dB.
- At 1,000 Hz the correction is 0 dB by definition.
- At 2,000 Hz about +1.2 dB and at 4,000 Hz about +1.0 dB, the small boost region.
- At 8,000 Hz about -1.1 dB and at 16,000 Hz about -6.6 dB.
A-weighting: frequently asked questions
What is A-weighting?
A-weighting is a frequency-dependent correction applied to sound level measurements to approximate the loudness perception of the human ear at moderate levels. It attenuates low and very high frequencies and is defined by the IEC 61672-1 standard. The corrected reading is reported in dB(A) and is the basis for most occupational and environmental noise limits.
What is the A-weighting formula?
The A-weighting transfer function uses fixed pole frequencies of 20.598997, 107.65265, 737.86223 and 12194.217 Hz. R_A(f) = (12194.217^2 * f^4) / ((f^2 + 20.598997^2) * sqrt((f^2 + 107.65265^2)(f^2 + 737.86223^2)) * (f^2 + 12194.217^2)). The weighting in dB is A(f) = 20 * log10(R_A(f)) + 2.00, normalized to 0 dB at 1 kHz.
Why is the correction roughly 0 dB at 1 kHz?
The A-weighting curve is defined to pass through 0 dB at 1,000 Hz by adding a normalization offset of about +2.00 dB to the raw transfer function. This means a 1 kHz tone reads the same in dB and dB(A). Frequencies below 1 kHz get progressively larger negative corrections, for example about -16 dB at 125 Hz.
How do I apply the correction to a measurement?
Add the A-weighting value (which is negative below about 1 kHz) to the unweighted (linear or Z-weighted) sound pressure level at that frequency. For example, a 60 dB tone at 125 Hz with a -16.2 dB correction reads about 43.8 dB(A). Broadband signals require summing the weighted band levels on an energy basis.
When should I use C-weighting instead of A-weighting?
C-weighting is much flatter and is used for peak measurements and high-level sounds where low-frequency content matters, such as impulse noise or loud music. A-weighting is preferred for general environmental and occupational exposure assessment at moderate levels because it better matches hearing sensitivity there. Both are defined in IEC 61672-1.
Official sources
- NIOSH (CDC): Noise and Occupational Hearing Loss.
- NIST: National Institute of Standards and Technology.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.