The ear has the remarkable ability to handle an enormous range of sound levels. In order to express levels of sound meaningfully in numbers that are more manageable, a logarithmic scale is used, rather than a linear one. This scale is the decibel scale. Zero decibels (0 dB) is the quietest sound audible to a healthy human ear. From there, every increase of 3 dB represents a doubling of sound intensity, or acoustic power.
Sound pressure converted to the decibel scale is called sound pressure level (Lp).
The decibel scale is a logarithmic scale used to make quantities with a wide range of values more manageable. The range of acoustic pressures that the human ear can detect is very wide - from the lower limit of hearing at around 20 micro Pa (2 x 10-5 Pa) to the threshold of pain at around 20 Pa.
Converting pressure to decibels creates a more manageable measuring and comparison yardstick. Converting the very wide range of values into a logarithmic scale changes the range of values to the more manageable range of 0 dB to 140 dB where 0 dB is roughly the lowest level a normal person can hear.
As you can see from the diagram decibels is a log function of pressure. Which means small increases in decibels map to larger and larger increases in pressure. The human ear is designed to hear very soft sounds with very little pressure to be able to cope with very high pressure noise. The spread of pressure in micropascals ranges from 20 Mpa to 100 million Mpa.