Unit Converters · Browser · Free

dBm Converter

Four Power boxes take a number and a Convert button shows that same power in mW, W, dBm and dBW. The whole conversion happens in your browser.

What this tool does

The form holds four number fields, each labelled Power, and a Convert button. A dBm figure is a power stated on a decibel scale against one milliwatt, and this tool moves a power between milliwatts (mW), watts (W), dBm and dBW.

Nothing is worked out beforehand: the form computes only when you press Convert, and the answers then show up in cards below the button, one card for each unit. A 100 mW input returns Power: 100 mW; Power: 0.1 W; Power: 20 dBm; Power: -10 dBW, and a 3 dBm input returns Power: 1.99526231496888 mW; Power: 0.00199526231496888 W; Power: 3 dBm; Power: -27 dBW.

Copy writes a result together with its unit to the clipboard, and Clear resets the form so you can start again with a new number.

The dBm conversion formula

From milliwatts: P(dBm) = 10 × log10(P(mW) / 1 mW). From watts: P(dBm) = 10 × log10(P(W) / 1 W) + 30. From dBW: P(dBm) = P(dBW) + 30. Going the other way, from dBm back to milliwatts: P(mW) = 1 mW × 10^(P(dBm) / 10).

The results above follow those lines exactly: P(dBm) = 10 × log10(100 mW / 1 mW) = 20 dBm, P(mW) = 1 mW × 10^(20 / 10) = 100 mW, P(dBm) = 10 × log10(100 W / 1 W) + 30 = 50 dBm, and P(dBm) = 20 dBW + 30 = 50 dBm.

Because of the +30 step, a dBm figure sits 30 above the same power in dBW, so 20 dBm matches -10 dBW and 50 dBm matches 20 dBW. A small value works the same way: P(mW) = 1 mW × 10^(3 / 10) = 1.99526231496888 mW.