KinexiaLEARN PHYSICS

Decibel (dB)

Quantity: Level (logarithmic ratio) · Category: Non-SI

The decibel is a logarithmic unit for expressing ratios — of power, intensity or amplitude. Because human hearing and many physical processes span enormous ranges, the logarithmic scale keeps the numbers manageable.

Relation to SI

L(dB) = 10·log₁₀(P/P₀) — dimensionless ratio

Examples

  • A whisper is about 30 dB; normal speech about 60 dB.
  • Every 10 dB means ten times the sound intensity.
  • A rock concert at 110 dB is 100,000 times more intense than 60 dB speech.