A decibel (dB) is the internationally adopted unit for the relative intensity of sound. The sound intensity of 0 decibel is the threshold of human hearing, 10-16 watts/cm2. This corresponds to a pressure of 2 X 10-5 newtons/m2 or 2 billionths of atmospheric pressure. The ear is extremely sensitive! The decibel scale is a logarithmic scale, meaning for every 10 decibels, the intensity is increased by a factor of ten. For example, a change from 30 decibels to 40 decibels means the sound will be ten times more intense. A change from 30 decibels to 50 decibels would mean the new sound would be one hundred times more intense.
The following chart shows a typical sound environment, how many times louder those levels are than the threshold of human hearing, and the relative intensity of that sound compared to the threshold of hearing.
| Sound |
Times More Intencse |
Relative Intensity (dB) |
| Loss of hearing |
1 x 1015 |
150 |
| Rocket launch |
1 x 1014 |
140 |
| Jet engine 50 meters away |
1 x 1013 |
130 |
| Threshold of pain |
1 x 1012 |
120 |
| Rock concert |
1 x 1011 |
110 |
| Lawnmower |
1 x 1010 |
100 |
| Factory |
1 x 109 |
90 |
| Motorcycle |
1 x 108 |
80 |
| Automobiles driving by |
1 x 107 |
70 |
| Vacuum cleaner |
1,000,000 |
60 |
| Normal speech |
100,000 |
50 |
| Library |
10,000 |
40 |
| Close whisper |
1,000 |
30 |
| Leaves rustling in the wind |
100 |
20 |
| Breathing/whisper 5 meters away |
10 |
10 |
| Threshold of hearing |
0 |
0 |
