dBm – a unit of absolute level of reference to the power of 1 mW (milliwatt); a dBmW expression ought to be used according to the rule but the expression of dBm is exceptionally used here.
This unit is commonly used in telecommunications (e.g. an output power of an access point is provided) or it is used in designing WLAN network. A unit expressed in dB informs us how much this power is lower than power expressed in 1 mW. The level 0 dB corresponds to 1 mW (milliwatt).
A commonly used power formula is used in converting mW into dBm.
P(ref) – a referential value, which is a reference measure, which in this case is 1 mW (milliwatt)
A power formula in dBm which is more straightforward visually:
Example Let us convert 10 mW into dBm:
If we want to convert dBm into mW, we use the following formula:
Example Let us convert 20 dBm into mW (milliwatts).
Tab. 1. Conversion of dBm into mW - wide range
-30 dBm
0,001 mW
-20 dBm
0,01 mW
-10 dBm
0,1 mW
0 dBm
1 mW
10 dBm
10 mW
20 dBm
100 mW
30 dBm
1000 mW
40 dBm
10000 mW
50 dBm
100000 mW
60 dBm
1000000 mW
70 dBm
10000000 mW
80 dBm
100000000 mW
Tab. 2. Conversion of dBm into mW - detailed range
14 dBm
25,119 mW
16 dBm
39,811 mW
18 dBm
63,096 mW
20 dBm
100,000 mW
22 dBm
158,489 mW
24 dBm
251,189 mW
26 dBm
398,107 mW
28 dBm
630,957 mW
30 dBm
1000,000 mW
We can also convert power to voltage very easily: dBm into dBµV and dBmV. In order to convert voltage from power we have to know internal impedance. In terrestrial, cable and industrial television systems, impedance of 75 ohm is used. In radio systems it is 50 ohm.
The formulas for these two environments are provided below:
Example We convert 20 dBm into dBµV (for impedance of 50 ohm)
dBµV = 106,98 + 20 = 126,98 dBµV
Netto:
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Brutto:
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Paino:
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