Loudness is measured on a logarithmic scale. This means that an increase of 10 decibels (dB) represents a 10-fold increase in sound intensity and a doubling of the perceived loudness. Thus, 20 dB is 100 times the intensity of 0 dB and seems 4 times as loud; 30 dB is 1,000 times the intensity of 0 dB and seems 8 times as loud.
Faintest sound heard by human ear
Whisper, quiet library
Normal conversation, sewing machine, or typewriter
Lawnmower, shop tools, or truck traffic (90 dB for 8 hours per day is the maximum exposure without protection*)
Chainsaw, pneumatic drill, or snowmobile (2 hours per day is the maximum exposure without protection)
Sandblasting, loud rock concert, or automobile horn (15 minutes per day is the maximum exposure without protection)
Gun muzzle blast or jet engine (noise causes pain, and even brief exposure injures unprotected ears, and injury may occur even with hearing protectors)
Rocket launching pad
*This level is the mandatory federal standard, but protection is recommended for anything more than very brief exposure to sound levels above 85 dB.