What is a decibel, and how is it measured?

The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel scale is a little odd because the human ear is incredibly sensitive. Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound. That's a big difference!

On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. Here are some common sounds and their decibel ratings:

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  • Near total silence - 0 dB
  • A whisper - 15 dB
  • Normal conversation - 60 dB
  • A lawnmower - 90 dB
  • A car horn - 110 dB
  • A rock concert or a jet engine - 120 dB
  • A gunshot or firecracker - 140 dB

You know from your own experience that distance affects the intensity of sound -- if you are far away, the power is greatly diminished. All of the ratings above are taken while standing near the sound.

Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. You know that you are listening to an 85-dB sound if you have to raise your voice to be heard by somebody else. Eight hours of 90-dB sound can cause damage to your ears; any exposure to 140-dB sound causes immediate damage (and causes actual pain). See this page for an exposure "ruler."

 

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Originally Published: Apr 1, 2000

Decibel FAQ

What is a decibel?
A decibel is a measure of sound intensity and amplitude using the decibel (dB) scale. The amplitude of a sound depends on its loudness.
How do you calculate decibels?
Calculate the logarithm of the power ratio, then multiple the outcome by 10 to identify the number of decibels.
How many decibels is loud?
A normal conversation is around 60 dB and more than 85 dB can harm your hearing over time. If you’re too close, a loud noise over 120 dB can inflict instant damage to your ears.
Is 100 dB too loud?
Yes, it is too loud for prolonged exposure as anything louder than 85 dB can cause hearing loss. For reference, a farm tractor, motorcycle and jackhammer are all around 100 dB.

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