Short answer: dB is a general decibel level with no hearing adjustment; dBA (or dB(A)) is the same sound level after A-weighting, a filter that turns down low and very high frequencies the way human ears do. For speech and most everyday sounds, dB and dBA are within a few decibels; for bass-heavy sounds, dBA reads much lower.
You will see both on sound meters, product labels and safety rules. This guide explains what each one means, why hearing limits use dBA, how much the numbers can differ, and which setting to choose when you measure. For the A-versus-C comparison, see dBA vs dBC.
dB vs dBA vs dBC at a Glance
| dB (unweighted, dB SPL or dBZ) | dBA (A-weighted) | dBC (C-weighted) | |
|---|---|---|---|
| What it measures | Total sound pressure level at all frequencies | Sound level adjusted to human hearing at moderate levels | Sound level with only a slight adjustment; keeps the bass |
| Low frequencies (bass) | Counted in full | Strongly reduced (−26 dB at 63 Hz) | Almost fully counted (−0.8 dB at 63 Hz) |
| Used for | Physics, acoustics research, frequency analysis | Hearing safety, workplace limits, traffic, neighbour noise, appliance ratings | Peaks, concerts, subwoofers, low-frequency noise |
| Typical reading for speech | About the same as dBA | Reference | About the same |
| Typical reading for a truck idling | Highest | Lowest (often 10+ dB lower) | Close to unweighted |
What Does dB Mean on Its Own?
A decibel is a ratio on a logarithmic scale, so “dB” always needs a reference. For sound in air, the usual reference is 20 µPa, and the level is called dB SPL; see sound pressure level. When a meter shows plain dB, it normally means unweighted SPL, now called Z-weighting (flat from 10 Hz to 20 kHz). In other fields, dB can be relative to a voltage, a power or a digital full scale, which is why you also see dBV, dBm and dBFS; the decibel units guide lists them all. If you need a refresher on the scale itself, read what a decibel is.
What Is dBA (A-Weighting)?
Your ears are much less sensitive to deep bass and the very highest pitches than to the mid-range, especially at everyday levels. A-weighting, defined in the sound level meter standard IEC 61672-1, applies a correction at each frequency before the level is added up:
| Frequency | 63 Hz | 125 Hz | 250 Hz | 500 Hz | 1 kHz | 2 kHz | 4 kHz | 8 kHz |
|---|---|---|---|---|---|---|---|---|
| A-weighting | −26.2 | −16.1 | −8.6 | −3.2 | 0 | +1.2 | +1.0 | −1.1 |
So a 63 Hz hum that measures 70 dB unweighted reads only about 44 dBA, while a 2 kHz whistle at 70 dB reads about 71 dBA. That matches how loud the two actually seem. Frequency and level are separate properties of a sound (see dB vs Hz), and a frequency analyzer shows which frequencies a sound contains.
Why Safety Standards Use dBA
A-weighting tracks both how loud a sound seems and how much it can harm hearing, because the inner ear is also less vulnerable to low frequencies at the same pressure. That is why the 8-hour limits of NIOSH (85 dBA) and OSHA (90 dBA), the EU action values (80 and 85 dBA), environmental noise guidelines and most appliance labels are all in dBA. The one exception is short, sharp peaks such as gunshots, which are limited by C-weighted or unweighted peak levels. See the NIOSH and OSHA noise limits, is 85 dB dangerous?, or check your own day with the noise exposure calculator.
How Much Do dB and dBA Differ? Real Examples
| Sound | Unweighted dB (typical) | dBA (typical) | Why |
|---|---|---|---|
| Conversation | 61–63 | 60 | Energy mostly in the mid-range |
| Vacuum cleaner | 72–75 | 70–72 | Broad noise with some low rumble |
| Road traffic at 15 m | 78–82 | 70–75 | Engine and tyre rumble below 250 Hz |
| Diesel engine idling | 90 | 78–80 | Strong low-frequency content |
| Bass through a wall from a neighbour’s stereo | 55–65 | 35–45 | Almost all energy below 150 Hz |
These are typical figures; your readings will vary. When the gap is 10 dB or more, low-frequency sound dominates and dBA alone can understate how annoying the noise is. The decibel chart lists common sounds in dBA.
Is dBA Louder or Quieter Than dB?
For the same sound, dBA is almost always the same or lower than unweighted dB, because A-weighting only removes energy at frequencies outside the mid-range; it adds at most about 1 dB between 1 and 5 kHz. There is no fixed conversion factor: the difference depends entirely on the sound’s frequency content, so you have to measure both or analyse the spectrum.
Other “dB” Labels You May See
- dB SPL: unweighted sound pressure level re 20 µPa. Convert it to pascals with the SPL converter.
- dBC: C-weighted level for peaks and bass (compared in the table above).
- dBFS: digital level relative to full scale in recordings; see dB vs dBFS.
- dB HL: hearing level on an audiogram, where 0 dB HL is average normal hearing at each frequency. Our online hearing test shows a relative version.
- LAeq: the A-weighted average level over a period, the number most regulations use.
Which Setting Should You Use When You Measure?
Use dBA to answer “how loud is it?” or “is it safe?”, and to compare with any guideline, limit or product rating. Use dBC or unweighted dB for bass, music, subwoofers, engines and peaks. The free sound decibel meter shows dB(A), dB(C) and dB(Z) side by side, so you can see the gap directly. For more reliable numbers, calibrate your microphone and read about online decibel meter accuracy; phone microphones are weak at deep bass, so unweighted readings of very low sounds are less reliable than dBA.
Frequently Asked Questions
Is dB the same as dBA?
No. dBA is a decibel level with A-weighting applied. For mid-frequency sounds the numbers are close; for bass-heavy sounds dBA is lower.
Why is my dBA reading lower than dB?
Because the sound contains low frequencies that A-weighting reduces. A large gap (10 dB or more) means strong bass or rumble.
Is 85 dB the same as 85 dBA?
Only if the sound is mostly mid-range. Hearing limits such as 85 dBA for 8 hours are A-weighted, so always compare dBA with dBA.
What does the A in dBA stand for?
It names the weighting curve. A, B and C were originally based on equal-loudness curves at low, medium and high levels; A-weighting is the one used for most noise measurement today.