Difference Between dB and dBm

dB vs dBm

dB and dBm are units related to measurements in sound and acoustics. The notations dB and dBm are used to represent decibel and the ratio between the decibel level and a standard decibel level of 1 milliwatt. The unit decibel is used to measure the sound intensity level of a wave. These units are widely used in fields related to acoustics and radio technology. In this article, we are going to discuss what dB and dBm are, their definitions, applications of dB and dBm, the similarities and differences between dB and dBm.


The base unit of decibel is “bel”, which is a very rarely used unit. The unit decibel is directly connected to the intensity of a wave. The intensity of a wave at a point is the energy carried by the wave per unit time per unit area at that point. The unit decibel is used to measure the intensity level of a wave.

The decibel value is the logarithmic ratio of the intensity of the wave to a certain reference point. For the sound waves, the reference point is 10-12 watts per square meter. This is the minimum hearing threshold of a human ear. The sound intensity level at that point is zero.

Decibel is a very useful mode when it comes to fields such as amplifiers. This method can be used to convert multiplications and ratios into subtractions and additions. The decibel is a dimensionless unit. The unit decibel cannot be expanded using basic dimensions of [L], [T] and [M]. The power carried by a wave depends on the amplitude of the wave for a classical wave. The lower threshold of 10-12 watts per square meter used as the reference point for the decibel value is the lowest power level that is sufficient to create a hearing stimulation in a human ear.

dBm or dBmW

dBm is also known as dBmW is a notation used indicate a ratio of two power levels. Decibel uses the lower threshold power level of 10-12 watts as the reference power level. The unit dBm uses 1 milliwatt as the reference power level instead of the 10-12 watts used in dB.

The formula for calculating the sound intensity level with respect to 1 milliwatt is dBm = 10 log (p / 10-3) where p is the power emitted per unit area. dBm is also a dimensionless unit which cannot be expressed using basic dimensions. dBm is a unit widely used in the field of radio technology to measure sound levels.


What is the difference between dB and dBm?

• The unit dB uses the lower threshold power of hearing as the reference power level, whereas dBm uses 1 milliwatt as the reference power level.

• Same power level measured with dB and dBm separately gives a difference of 9 dB.