What Is a Decibel (dB)?
A complete guide to the decibel scale, how it works, and what it means for your hearing.
Definition
A decibel (dB) is a unit that expresses the intensity of a sound relative to a reference level — typically the threshold of human hearing (0 dB). It's used in acoustics, audio engineering, telecommunications, and hearing science.
Why the scale is logarithmic
Human hearing spans a huge range — the loudest sound we can tolerate is roughly a trillion times more intense than the quietest sound we can hear. A linear scale would be impractical, so we use a logarithmic one:
- +10 dB = 10× more intense
- +20 dB = 100× more intense
- +30 dB = 1,000× more intense
Perceptually, +10 dB sounds roughly twice as loud to a human. This is why a 90 dB lawn mower sounds "twice as loud" as an 80 dB vacuum cleaner even though it's 10× more physically intense.
Common decibel levels
Here are some reference points on the dB scale:
- 0 dB — threshold of human hearing
- 30 dB — whisper
- 60 dB — normal conversation
- 75 dB — vacuum cleaner
- 85 dB — hearing damage threshold with prolonged exposure
- 90 dB — lawn mower
- 110 dB — rock concert
- 140 dB — jet engine at takeoff
See the full dB chart or browse decibel levels of common sounds.
dB and hearing damage
Sustained exposure above 85 dB causes permanent hearing loss over time. The NIOSH guideline uses a 3 dB exchange rate — every 3 dB above 85 halves the safe exposure time. Track your daily dose with our noise exposure calculator.
Different dB weightings
You may see dBA, dBC, or dB SPL. These are different weightings that emphasize different parts of the frequency spectrum. dBA mimics the sensitivity of human hearing and is the most common weighting for occupational safety and everyday measurements.
Try it yourself
Use our free browser-based online decibel meter to measure the sounds around you right now.