Know Your Decibels and Watts

In the RF world, there are multiple uses of a variety of specifications in various forms where the units are in decibels of some type. It can be confusing by itself and then often when talking about power output, those in the know will switch from decibels to watts. This brief article strives to help you understand the ins and outs of decibels and watts.

dBW (Decibel-Watt)

dBW definition

dBW or decibel-watt is a unit of power in decibel scale, referenced to 1 watt (W).

The power in decibel-watts (P(dBW)) is equal to 10 times base 10 logarithm of the power in watts (P(W)):
P(dBW) = 10 ⋅ log10( P(W) / 1W)

The power in watts (P(W)) is equal to 10 raised by the power in decibel-watts (P(dBW)) divided by 10:
P(W) = 1W ⋅ 10(P(dBW)/ 10)

1 watt is equal to 0 dBW:
1W = 0dBW

1 milliwatt is equal to -30dBW:
1mW = 0.001W = -30dBW

How to Convert dBW to dBm (dB milliwatts)

The power in dBm is equal to the base 10 logarithm of the power in watts (W):
P(dBm) = P(dBW) + 30

Example

What is the power in dBm for power consumption of 20dBW? Solution:
P(dBm) = 20dBW + 30 = 50dBm

dB to Watts Conversion Table

Power (dBW) Power (dBm) Power (Watt)
-130 dBW -100 dBm 0.1 pW
-120 dBW -90 dBm 1 pW
-110 dBW -80 dBm 10 pW
-100 dBW -70 dBm 100 pW
-90 dBW -60 dBm 1 nW
-80 dBW -50 dBm 10 nW
-70 dBW -40 dBm 100 nW
-60 dBW -30 dBm 1 μW
-50 dBW -20 dBm 10 μW
-40 dBW -10 dBm 100 μW
-30 dBW 0 dBm 1 mW
-20 dBW 10 dBm 10 mW
-10 dBW 20 dBm 100 mW
-1 dBW 29 dBm 0.794328 W
0 dBW 30 dBm 1.000000 W
1 dBW 31 dBm 1.258925 W
10 dBW 40 dBm 10 W
20 dBW 50 dBm 100 W
30 dBW 60 dBm 1 kW
40 dBW 70 dBm 10 kW
50 dBW 80 dBm 100 kW
60 dBW 90 dBm 1 MW
70 dBW 100 dBm 10 MW
80 dBW 110 dBm 100 MW
90 dBW 120 dBm 1 GW
100 dBW 130 dBm 10 GW
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