dBm in telecom application and unit conversions: “dBm” to “mW”

What is “dBm”?

  dBm (sometimes dBmW or decibel-milliwatts) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt (1000 mW).

EDFA CATV FTTH Triple play equipment package

dBm (power) used in EDFA CATV Triple play equipment

  Since it is referenced to the watt, it is an absolute unit, used when measuring absolute power. By comparison, the decibel (dB) is a dimensionless unit, used for quantifying the ratio between two values, such as signal-to-noise ratio.

  In audio and telephony, dBm is typically referenced relative to a 600 ohm impedance, while in radio frequency work dBm is typically referenced relative to a 50 ohm impedance.

Unit conversions: “dBm” to “mW”

  A power level of 0 dBm corresponds to a power of 1 milliwatt. A 3 dB increase in level is approximately equivalent to doubling the power, which means that a level of 3 dBm corresponds roughly to a power of 2 mW. For each 3 dB decrease in level, the power is reduced by about one half, making −3 dBm correspond to a power of about 0.5 mW.

  To express an arbitrary power P in mW as x in dBm, or vice versa, the following equivalent expressions may be used:

Equivalent expressions: dBm to mW

dBm mW Equivalent Expressions

  where P is the power in W and x is the power level in dBm. Below is a table summarizing useful cases:

Power levelPowerNotes
80 dBm100 kWTypical  transmission power  of  FM radio  station with 50-kilometre (31 mi) range
62 dBm1.588 kW = 1,588 W1,500 W is the maximum legal power output of a U.S.  ham radio  station. [3]
60 dBm1 kW = 1,000 WTypical combined radiated RF power of microwave oven elements
55 dBm~300 WTypical single-channel RF output power of a Ku-Band GEO-stationary satellite
50 dBm100 WTypical total thermal radiation emitted by a human body, peak at 31.5 THz (9.5 micron)
Typical maximum output RF power from a ham radio HF transceiver
40 dBm10 WTypical PLC (Power Line Carrier) transmit power
37 dBm5 WTypical maximum output RF power from a handheld ham radio VHF/UHF transceiver
36 dBm4 WTypical maximum output power for a Citizens' band radio station (27 MHz) in many countries
33 dBm2 WMaximum output from a  UMTS / 3G  mobile phone (Power class 1 mobiles)
Maximum output from a GSM850/900 mobile phone
30 dBm1 W = 1,000 mWDCS or GSM 1,800/1,900 MHz mobile phone.  EIRP  IEEE 802.11a (20 MHz-wide channels) in either 5 GHz Subband 2 (5,470–5,725 MHz) provided that transmitters are also IEEE 802.11h-compliant,  or   U-NII -3 (5,725–5,825 MHz). The former is EU only, the latter is US only.
29 dBm794 mW
28 dBm631 mW
27 dBm500 mWTypical cellular phone transmission power
Maximum output from a UMTS/3G mobile phone (Power class 2 mobiles)
26 dBm400 mW
25 dBm316 mW
24 dBm251 mWMaximum output from a UMTS/3G mobile phone (Power class 3 mobiles)
1,880–1,900 MHz  DECT  (250 mW per 1,728 kHz channel).  EIRP  for Wireless LAN IEEE 802.11a (20 MHz-wide channels) in either the 5 GHz Subband 1 (5,180–5,320 MHz) or  U-NII -2 & -W ranges (5,250–5,350 MHz & 5,470–5,725 MHz respectively). The former is EU only, the latter is US only.
23 dBm200 mWEIRP  for IEEE 802.11n Wireless LAN 40 MHz-wide (5 mW/MHz) channels in 5 GHz subband 4 (5,735–5,835 MHz, US only) or 5 GHz subband 2 (5,470–5,725 MHz, EU only). Also applies to 20 MHz-wide (10 mW/MHz) IEEE 802.11a Wireless LAN in 5 GHz Subband 1 (5,180–5,320 MHz)  if  also IEEE 802.11h compliant (otherwise only 3 mW/MHz → 60 mW when unable to dynamically adjust transmission power, and only 1.5 mW/MHz → 30 mW when a transmitter also cannot  dynamically select frequency ).
22 dBm158 mW
21 dBm125 mWMaximum output from a UMTS/3G mobile phone (Power class 4 mobiles)
20 dBm100 mWEIRP  for IEEE 802.11b/g Wireless LAN 20 MHz-wide channels in the 2.4 GHz  Wi-Fi / ISM band  (5 mW/MHz).
Bluetooth  Class 1 radio. Maximum output power from unlicensed  AM transmitter  per U.S.  Federal Communications Commission  (FCC) rules 15.219. [4]
19 dBm79 mW
18 dBm63 mW
17 dBm50 mW
15 dBm32 mWTypical Wireless LAN transmission power in laptops
10 dBm10 mW
7 dBm5.0 mWCommon power level required to test the automatic gain control circuitry in an AM receiver
6 dBm4.0 mW
5 dBm3.2 mW
4 dBm2.5 mWBluetooth Class 2 radio, 10 m range
3 dBm2.0 mW
2 dBm1.6 mW
1 dBm1.3 mW
0 dBm1.0 mW = 1,000 µWBluetooth standard (Class 3) radio, 1 m range
−1 dBm794 µW
−3 dBm501 µW
−5 dBm316 µW
−10 dBm100 µWMaximum received signal power of wireless network (802.11 variants)
−20 dBm10 µW
−30 dBm1.0 µW = 1,000 nW
−40 dBm100 nW
−50 dBm10 nW
−60 dBm1.0 nW = 1,000 pWThe  Earth  receives one nanowatt per square metre from a  magnitude  +3.5  star [5]
−70 dBm100 pW
−73 dBm50.12 pW"S9" signal strength, a strong signal, on the  S-meter  of a typical  ham  or  shortwave  radio receiver
−80 dBm10 pW
−100 dBm0.1 pWMinimum received signal power of wireless network (802.11 variants)
−111 dBm0.008 pW = 8 fWThermal noise floor  for commercial  GPS  single channel signal bandwidth (2 MHz)
−127.5 dBm0.178 fW = 178 aWTypical received signal power from a GPS satellite
−174 dBm0.004 aW = 4 zWThermal noise floor for 1 Hz bandwidth at room temperature (20 °C)
−192.5 dBm0.056  zW = 56  yWThermal noise floor for 1 Hz bandwidth in outer space (4 kelvins)
−∞ dBm0 WZero power is not well-expressed in dBm (value is negative infinity)

dBm: an industry standard application unit

  The signal intensity (power per unit area) can be converted to received signal power by multiplying by the square of the wavelength and dividing by 4π (see Free-space path loss).

  In United States Department of Defense practice, unweighted measurement is normally understood, applicable to a certain bandwidth, which must be stated or implied.

  In European practice, psophometric weighting may be, as indicated by context, equivalent to dBm0p, which is preferred.

  In audio, 0 dBm often corresponds to approximately 0.775 volts, since 0.775 volts dissipates 1 mW in a 600 Ω load.[6] dBu measures against this reference voltage without the 600 Ω restriction. Conversely, for RF situations with a 50 Ω load, 0 dBm corresponds to approximately 0.224 volts since 0.224 volts dissipates 1 mW in a 50 Ω load.

  The dBm is not a part of the International System of Units and therefore is discouraged from use in documents or systems that adhere to SI units (the corresponding SI unit is the watt). However the straight decibel (dB), being a unitless ratio of two numbers, is perfectly acceptable.

  Expression in dBm is typically used for optical and electrical power measurements, not for other types of power (such as thermal). A listing by power levels in watts is available that includes a variety of examples not necessarily related to electrical or optical power.

  The dBm was first proposed as an industry standard in the paper “A New Standard Volume Indicator and Reference Level”.

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