dBm - dBw Watts conversion chart

- chart or table to provide a conversion between power measured in dBm or dBW and power measured in watts. dBm and dBW are widely used in conjunction with RF test equipment.

The decibel is widely used in radio and electronics design calculations. When measuring radio frequency, or RF power, it is often easier to have a measurement made in a way that it is easy to compare the two power levels. As a result many power levels are specified in dBm or dBW, and much RF test equipment including power meters or spectrum analysers have calibrations in dBm or dBW. Often RF components such as mixers, oscillators and the like, as well as the interfaces between modules in RF equipment have their levels specified in dBm or dBW. Radio transmitters may also have their power levels expressed in this way.

What are dBm and dBW?
In itself a decibel is not an absolute level. It is purely a comparison between two levels, and on its own it cannot be used to measure an absolute power level. As a result of this the quantities of dBm and dBW are used:

• dBm - This is a power expressed in decibels relative to one milliwatt.



• dBW - This is a power expressed in decibels relative to one watt.

From this it can be seen that a power level of 10 dBm is ten dB above one milliwatt, i.e. 10 mW. Similarly a power level of 20 dBW is 100 times that of one watt, i.e. 100 watts.

A more extensive conversion table of dBm, dBW and power is given below:

dBm	dBW	Watts	Terminology
+100	+70	10 000 000	10 Megawatts
+90	+60	1 000 000	1 Megawatt
+80	+50	100 000	100 kilowatts
+70	+40	10 000	10 kilowatts
+60	+30	1 000	1 kilowatt
+50	+20	100	100 watts
+40	+10	10	10 watts
+30	0	1	1 watt
+20	-10	0.1	100 milliwatts
+10	-20	0.01	10 milliwatts
0	-30	0.001	1 milliwatt
-10	-40	0.0001	100 microwatts
-20	-50	0.00001	10 microwatts
-30	-60	0.000001	1 microwatt
-40	-70	0.0000001	100 nanowatts
-50	-80	0.00000001	10 nanowatts
-60	-90	0.000000001	1 nanowatt

The use of the values dBm and dBW is widespread. They are found as direct calibration scales on many items of RF test equipment, often being used in preference to the more elementary basic units of watts or milliwatts. Items of RF test equipment including power meters and RF spectrum analyzers in particular use these units, and many RF components are also specified in terms of power levels in dBm or dBW.