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What Does dBA Mean on a Sound Meter?

The A in dBA is a filter that turns down the bass and the extreme treble before the meter adds up the sound, because ears do the same. It makes the number track annoyance and hearing risk better than a flat measurement would.

By the Akermin Editorial Team · 2 min read

dBA means decibels measured with A-weighting, a filter that reduces the meter’s sensitivity to low frequencies (below about 500 Hz) and very high frequencies (above about 10 kHz) to approximate how the human ear responds at moderate levels. A 100 Hz tone that measures 70 dB unweighted reads about 51 dBA; a 1 kHz tone reads the same either way. Nearly all noise regulations, workplace exposure limits and equipment specifications use dBA because it tracks loudness and hearing risk better than the raw level.

Why weight at all

Ears are not equally sensitive across frequencies. A 60 Hz hum needs far more sound energy to seem as loud as a 1 kHz tone; above 10 kHz sensitivity falls off again. A meter that simply adds up all the energy (Z-weighting, or “flat”) would report a rumbling air handler and a shrill alarm as equally loud when the alarm is far more intrusive. The A-weighting curve, derived from equal-loudness measurements made in the 1930s, corrects for this.

The A-weighting curve

Frequency A-weighting adjustment
31.5 Hz −39 dB
63 Hz −26 dB
125 Hz −16 dB
250 Hz −9 dB
500 Hz −3 dB
1 kHz 0 dB
2 kHz +1 dB
4 kHz +1 dB
8 kHz −1 dB
16 kHz −7 dB

A, C and Z compared

  • A: hearing-like; the default for limits and specifications.
  • C: nearly flat from 30 Hz to 8 kHz with gentle roll-off; used for peak (LCpeak) limits and for low-frequency noise assessments. A large gap between dBC and dBA readings (more than about 15 dB) signals strong low-frequency content.
  • Z: flat, no weighting; used for spectrum analysis and research.

Typical dBA levels

Source Approximate level
Quiet bedroom at night 25 to 30 dBA
Library, quiet office 40 dBA
Normal conversation at 1 m 60 dBA
Vacuum cleaner, busy office 70 dBA
Busy road, kitchen blender 80 dBA
Workplace 8-hour exposure limit (many jurisdictions) 85 dBA
Lawn mower, motorcycle 90 to 95 dBA
Chainsaw, rock concert 100 to 110 dBA

Reading it on a meter

Set the weighting switch to A unless a specification says otherwise. Pair it with the required time response (fast, slow) or integration (LAeq for exposure, LAmax for events, LA90 for background). A reading labeled “LAeq,15min = 58 dBA” is the A-weighted equivalent continuous level over 15 minutes, which is the form most limits take. See what a sound level meter is for classes, calibration and method; instruments are in the environmental monitoring category.

Extech SL510 Sound Level Meter, 35-130 dB, Class 2

Extech SL510 Sound Level Meter, 35-130 dB, Class 2

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Decibel Meter, TopTes TS-501B Sound Level Meter with 2.25” Backlit LCD Screen, Portable SPL Tester with A/C Weighted, Range 30-130dB, MAX/MIN, Data Hold, Use for Home, Noisy Neighbor, Factory - Orange

Decibel Meter, TopTes TS-501B Sound Level Meter with 2.25” Backlit

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

What is the difference between dB and dBA?

dB (or dBZ) is the unweighted sound level. dBA applies the A-weighting filter, which reduces low-frequency and very high-frequency content before the level is calculated. For most everyday sounds, dBA is a few dB lower than dBZ.

Why do noise limits use dBA?

Because A-weighted levels correlate best with perceived loudness and with hearing damage for the frequency mix of typical noise. It has been the standard for occupational and environmental limits for decades.

When would I use dBC?

For peak levels (impulsive noise such as hammering or gunfire) and for low-frequency noise from subwoofers, plant and traffic rumble, where A-weighting understates what people hear.

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