DBm

dBm (sometimes dBmW) 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).

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.

Unit conversions

Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making -3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, or go in the other direction, the following equations may be used:

with P power in mW and x power ratio in dBm. Below is a table summarizing useful cases:

dBm level	Power	Notes
80 dBm	100 kW	Typical transmission power of FM radio station with 50 km range
60 dBm	1 kW = 1000 W	Typical combined radiated RF power of microwave oven elements
50 dBm	100 W	Typical thermal radiation emitted by a human body
40 dBm	10 W
36 dBm	4 W	Typical maximum output power for a Citizens' band radio station (27 MHz) in many countries
33 dBm	2 W	Maximum output from a UMTS/3G mobile phone (Power class 1 mobiles) Maximum output from a GSM850/900 mobile phone
30 dBm	1 W = 1000 mW	Typical RF leakage from a microwave oven - Maximum output power for DCS 1800 MHz mobile phone Maximum output from a GSM1800/1900 mobile phone
27 dBm	500 mW	Typical cellular phone transmission power Maximum output from a UMTS/3G mobile phone (Power class 2 mobiles)
26 dBm	400 mW
25 dBm	316 mW
24 dBm	250 mW	Maximum output from a UMTS/3G mobile phone (Power class 3 mobiles)
23 dBm	200 mW
22 dBm	160 mW
21 dBm	125 mW	Maximum output from a UMTS/3G mobile phone (Power class 4 mobiles)
20 dBm	100 mW	Bluetooth Class 1 radio, 100 m range (maximum output power from unlicensed FM transmitter). Typical wireless router transmission power.
15 dBm	32 mW	Typical WiFi transmission power in laptops.
10 dBm	10 mW
6 dBm	4.0 mW
5 dBm	3.2 mW
4 dBm	2.5 mW	Bluetooth Class 2 radio, 10 m range
3 dBm	2.0 mW	More precisely (to 8 decimal places) 1.9952623 mW
2 dBm	1.6 mW
1 dBm	1.3 mW
0 dBm	1.0 mW = 1000 琺	Bluetooth standard (Class 3) radio, 1 m range
-1 dBm	794 琺
-3 dBm	501 琺
-5 dBm	316 琺
-10 dBm	100 琺	Typical maximum received signal power (−10 to −30 dBm) of wireless network
-20 dBm	10 琺
-30 dBm	1.0 琺 = 1000 nW
-40 dBm	100 nW
-50 dBm	10 nW
-60 dBm	1.0 nW = 1000 pW
-70 dBm	100 pW	Typical range (−60 to −80 dBm) of wireless (802.11x) received signal power over a network
-80 dBm	10 pW
-100 dBm	0.1 pW
-111 dBm	0.008 pW = 8 fW	Thermal noise floor for commercial GPS single channel signal bandwidth (2 MHz)
-127.5 dBm	0.178 fW = 178 aW	Typical received signal power from a GPS satellite
-174 dBm	0.004 aW	Thermal noise floor for 1 Hz bandwidth at room temperature (20C)
-192.5 dBm	0.00004 aW	Thermal noise floor for 1 Hz bandwidth in outer space (4 kelvin)
-? dBm	0 W	Zero power is not well-expressed in dBm (value is negative infinity)

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 4? (see Free-space path loss).

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

DBm

Contents

Unit conversions

See also

References

External links