Decibel Shield

dBm to watts converter

dBm is power relative to one milliwatt, so watts = 10(dBm − 30) / 10. 0 dBm is 1 mW, 20 dBm is 100 mW, 30 dBm is 1 W and 40 dBm is 10 W: every 10 dB is ten times the power and every 3 dB about twice. Type dBm, or a power in W, mW, µW or kW, and the other updates.

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30 dBm is

1 W

  • 1 W
  • 1,000 mW
  • 0.00 dBW

dBm is power relative to 1 milliwatt: 0 dBm is 1 mW, 30 dBm is 1 W, and every 10 dB is ten times the power.

dBm to watts table

Power for each dBm value (dBW is dBm − 30)
dBmPowerdBW
−30 dBm 1 µW −60
−20 dBm 10 µW −50
−10 dBm 100 µW −40
0 dBm 1 mW −30
1 dBm 1.26 mW −29
2 dBm 1.58 mW −28
3 dBm 2 mW −27
4 dBm 2.51 mW −26
5 dBm 3.16 mW −25
6 dBm 3.98 mW −24
7 dBm 5.01 mW −23
8 dBm 6.31 mW −22
9 dBm 7.94 mW −21
10 dBm 10 mW −20
11 dBm 12.6 mW −19
12 dBm 15.8 mW −18
13 dBm 20 mW −17
14 dBm 25.1 mW −16
15 dBm 31.6 mW −15
16 dBm 39.8 mW −14
17 dBm 50.1 mW −13
18 dBm 63.1 mW −12
19 dBm 79.4 mW −11
20 dBm 100 mW −10
21 dBm 126 mW −9
22 dBm 158 mW −8
23 dBm 200 mW −7
24 dBm 251 mW −6
25 dBm 316 mW −5
26 dBm 398 mW −4
27 dBm 501 mW −3
28 dBm 631 mW −2
29 dBm 794 mW −1
30 dBm 1 W 0
31 dBm 1.26 W 1
32 dBm 1.58 W 2
33 dBm 2 W 3
34 dBm 2.51 W 4
35 dBm 3.16 W 5
36 dBm 3.98 W 6
37 dBm 5.01 W 7
38 dBm 6.31 W 8
39 dBm 7.94 W 9
40 dBm 10 W 10
41 dBm 12.6 W 11
42 dBm 15.8 W 12
43 dBm 20 W 13
44 dBm 25.1 W 14
45 dBm 31.6 W 15
46 dBm 39.8 W 16
47 dBm 50.1 W 17
48 dBm 63.1 W 18
49 dBm 79.4 W 19
50 dBm 100 W 20
51 dBm 126 W 21
52 dBm 158 W 22
53 dBm 200 W 23
54 dBm 251 W 24
55 dBm 316 W 25
56 dBm 398 W 26
57 dBm 501 W 27
58 dBm 631 W 28
59 dBm 794 W 29
60 dBm 1 kW 30

The formula

P(W) = 10(dBm − 30) / 10, and dBm = 10 × log10(P / 1 mW). The 30 is the thousand milliwatts in a watt. In dBW the reference is one watt, so dBW = dBm − 30.

Sources: ITU-R Recommendation V.574-5, Use of the decibel and the neper in telecommunications; MIT OpenCourseWare 6.101, The Decibel Unit of Measurement; UNSW Physclips, dB: What is a decibel?; Stanford CCRMA, DBV Scale.

dBm, dBW, dBu and dBV

None of these is a sound level. A level in the air is dB SPL, relative to 20 micropascals; the SPL calculator converts pressure to dB SPL and works out a speaker's level from its power.

Bluetooth power classes in dBm

Bluetooth radios are grouped by their maximum transmit power: Class 1 up to 100 mW (20 dBm), Class 2 up to 2.5 mW (4 dBm) and Class 3 up to 1 mW (0 dBm). Bluetooth Low Energy adds Class 1.5, up to 10 mW (10 dBm). The Bluetooth SIG gives the whole span as −20 dBm (0.01 mW) to +20 dBm (100 mW).

How many watts is 30 dBm?

30 dBm is exactly 1 watt. 33 dBm is about 2 W, 40 dBm is 10 W and 50 dBm is 100 W; 20 dBm is 100 mW and 0 dBm is 1 mW.

How many dBm is 1 watt?

One watt is 30 dBm, because it is a thousand milliwatts and 10 × log10(1,000) = 30. Half a watt is about 27 dBm and 2 W about 33 dBm.

What is the difference between dBm and dBW?

Only the reference: dBm is relative to one milliwatt and dBW to one watt. The same power is always 30 dB higher in dBm, so 0 dBW = 30 dBm = 1 W.

Is dBm the same as dBu?

No. dBm is a power. dBu is a voltage: 0 dBu is 0.775 V RMS, the voltage that puts 1 mW into a 600-ohm load, which is where the two meet. Into any other load the same dBu is a different power, so audio gear rated in dBu cannot be read as dBm unless the impedance is 600 ohms.