dB is often confused with dBm.

*They are very different. *

dB stands for deciBel and dBm stands for deciBel relative to 1 milliwatt. Let’s get into the details.

**What is dB?**

**dB is a relative measure of two power or amplitude levels**

It can be used in the following instances :

- Gain of an amplifier – the ratio of the amplifier output to input power
- Link margin – specifies the ratio between the received signal and the minimum detectable signal power
- Signal-to-noise ratio – often abbreviated as
**SNR**, this gives a measure of how much the signal power exceeds the noise - Antenna cable loss – what is the insertion loss of the RF cable that sits between the antenna and transmitter or receiver?

The equation for calculating amplifier gain in dB is

**Amplifier Gain _{dB} = 10*Log_{10}(Pout/Pin)**

Similarly, the Signal-to-noise ratio in dB is

**SNR _{dB} = 10*Log_{10}(P_{signal}/P_{noise})**

The dB scale presents a convenient method of representing large numbers. For instance 1000000000 = 90 dB. It is used in audio, radio and other engineering disciplines.

**What is dBm?**

**dBm is a measure of power level and is an absolute quantity**

The input or output power level of an RF circuit can be expressed in dBm.

Power in Watt (**P _{W}**) is calculated from dBm (

**P**) using the following formula:

_{dBm}**P _{Watt}=(10^{(PdBm/10)})/1000**

Example applications:

- Sensitivity of a Wi-Fi system – What is the lowest signal level at which your home or office wireless system is functional?
- Thermal noise power – used to determine the sensitivity of a radio receiver.

dBm is normally used in Radio Frequency and Optical Engineering Applications.

**Can dB be converted to dBm?**

No – dB cannot be converted to dBm. They are different from each other.

*However, the difference between two dBm quantities is a number in dB.*

For instance, the noise power in dBm can be subtracted from the signal power in dBm to give the SNR in dB.

**SNR _{dB} = Ps_{dBm} – Pn_{dBm}**

If the signal power is +10 dBm and the noise power is -50 dBm, the SNR is 60 dB.

**SNR _{dB}** represents the ratio between the two linear quantities of signal and noise power. Another example is the ratio between EIRP and ERP and the difference between the two in dBm.