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Decibel-Watt (dBW) Converter

A decibel-watt is a power level written on the decibel scale against a reference of 1 watt, where 100 W equals 20 dBW. Put your number in the matching Power box and press Convert to see that same power in mW, W, dBm and dBW.

What the converter does

The page holds four Power boxes and a Convert button. Enter your number in the box for the unit you are starting from - milliwatts, watts, dBm or dBW - and press Convert. Nothing on the page changes until the button is pressed.

The results appear in four cards below the button: the same power written in mW, in W, in dBm and in dBW. Enter Power: 40 as dBm and the cards read Power: 10000 mW; Power: 10 W; Power: 40 dBm; Power: 10 dBW. Because all four boxes are labelled Power, entering 100 in watts gives 20 dBW, whereas entering 100 in milliwatts gives -10 dBW, and entering 20 in dBW equals 100 W.

Copy writes a result and its unit to the clipboard, and Clear resets the form. The whole calculation happens in the browser, so nothing is uploaded.

dBW to watt formula

To turn dBW into watts, multiply 1 watt by 10 raised to the dBW number divided by 10. The worked line P(W) = 1 W × 10^(20 / 10) = 100 W shows that, and it belongs with the cards Power: 100000 mW; Power: 100 W; Power: 50 dBm; Power: 20 dBW.

Going the other way, the dBW number is 10 times the base-10 logarithm of the power in watts: P(dBW) = 10 × log10(100 W / 1 W) = 20 dBW. A number given in milliwatts is read against 1000 mW, so P(dBW) = 10 × log10(100 mW / 1000 mW) = -10 dBW.

dBm sits 30 above dBW on the same scale, so subtracting 30 moves between them: P(dBW) = 40 dBm - 30 = 10 dBW. Powers below 1 W land on the negative side of the scale, as in Power: 100 mW; Power: 0.1 W; Power: 20 dBm; Power: -10 dBW, and a small figure such as Power: -1 comes back as about 0.794328 W.