The sound is all around us and can be measured to protect and inform us, as some sounds are not safe. In fact, loud noise can actually damage our hearing. So, the intensity of a sound is measured using decibel. As the human ear is incredibly sensitive, you can hear everything from your fingertip brushing lightly over your skin to a loud thunderclap. As far powe> is concerned, the sound of the thunderclap is approximately 1,000,000,000,000 times more powerful than the smallest audible sound. That makes a huge difference!

Formulas to calculate Decibel

  • When power is given:

The most basic form for decibel calculations as given below:

  • When voltage and current are given:

Decibel Meter

Sound can be measured with a device called decibel meter. It measures and samples sound. Decibel meters are also known as sound-level meters. It can even be accessed on a smartphone through apps. Measuring the sound of an environment with a common device like a smartphone that many people always carry may help protect their ears more often.

The decibel (dB) is a unit used to express the ratio of two values of a physical quantity, often power or intensity. One decibel is one-tenth of one bel, a unit name named in honor of Alexander Graham Bell. This unit ‘bel’ is seldom used.

A decibel meter is used for acoustic measurements. Sound traveling in acoustic means that the sound is traveling through the air. This instrument is usually a small device with a microphone that measures noise meter. In acoustic, a diaphragm is a transducer intended to interconvert mechanical vibrations to sounds, or vice versa. The diaphragm present in the microphone reacts to the changes in air pressure due to sound waves.

decibel meter

This is another reason why this instrument is also referred to as a Sound Pressure Level (spl meter). In the diaphragm movement, the sound pressure deviation is converted into an electrical signal (V).

When a constant pressure is applied, a microphone can be traced by the voltage produced, called as the microphone sensitivity. Decibel meter uses the sensitivity of the microphone and converts the electrical signal accurately to sound pressure, and show the resulting level of sound pressure (decibels dB).

This instrument is usually used to measure noise and serves as a level meter. If human beings are exposed to loud noises for a brief period, it doesn’t cause much harm, but continuous exposure can do physical damage like eardrums damage.

Sound level meters are mostly used in noise pollution studies to analyze the quantification of various kinds of noise. Thus, this device helps to measure the intensity of the sound, which can measure the decibel of the sound, so that one can take effective measures to reduce it.

Decibel Scale


On the decibel scale, 0 dB is the smallest audible sound. 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. A noise level chart showing examples of sounds with dB levels ranging from 0 to 120 decibels.

Decibel Sound Source
10 Almost inaudible Normal Breathing
20 Audible Rustling Leaves, Mosquitoes
30 Very quiet Whisper
40 Quiet Stream, Refrigerator humming
50 Limited Sound Quiet office
55 Normal Sound Filtering coffee-maker
60 Fairly Quiet Normal conversation
70 Irritating Vacuum cleaner, Hairdryer
75 Constant Sound Dishwasher
80 Unpleasant City Traffic Noise
85 Loud Lawnmower
90 Extremely Unpleasant Violin
95 Noisy Farm Tractor
100 Extremely Unpleasant Train
105 Even Louder Large drum
110 Extremely Loud Symphony Orchestra
120 Extremely Loud Thunderclap, Boombox


  1. The decibel is mostly applied in acoustics
  2. It is used as a unit of sound pressure level. In this, the reference pressure in air is set as the threshold value of perception of a human. There are many comparisons that are used to describe separate levels of pressure.
  3. The decibel is used to express the ratios of power or amplitude in arithmetic ratios in electronics. The total gain of decibel can be easily calculated by adding up all the decibel gains.

Continue learning more about Sound and Decibel with more interesting examples and diagrams at BYJU’S.

Practise This Question

A particle of mass m is projected from the ground with an initial speed u0 at an angle α with the horizontal. At the highest point of its trajectory, it makes a completely inelastic collision with another identical particle, which was thrown vertically upward from the ground with the same initial speed u0. The angle that the composite system makes with the horizontal immediately after the collision is ?