Watts to dBm Converter
Convert watt to decibel-milliwatts instantly. Formula, worked steps and a full reference table.
How to use it
- Type the value in watt — the result updates as you type.
- Use Swap to flip the direction, or change either dropdown to convert between any two units.
- Click the result to copy it. The URL updates too, so you can bookmark or share the exact conversion.
Examples
| 1 W | 30 dBm |
| 5 W | 36.98970004 dBm |
| 10 W | 40 dBm |
| 100 W | 50 dBm |
One watt equals 30 decibel-milliwattses (dBm). To convert watts to decibel-milliwattses, multiply by 30; to go back the other way, multiply by 0.0012589254 instead.
The converter above does it as you type and shows the working underneath, so you can check the arithmetic rather than take the number on trust.
What watts and decibel-milliwattses actually measure
Watt (W) — The watt is the SI unit of power — one joule per second. Light bulbs, appliances, audio equipment and solar panels.
Decibel-milliwatts (dBm) — dBm is power on a logarithmic scale referenced to one milliwatt, so 0 dBm is exactly 1 mW. Radio, Wi-Fi signal strength and fibre optics.
Watts to dBm conversion table
The most common values, worked out in advance. Anything not listed can be typed straight into the converter.
| W | dBm |
|---|---|
| 1 W | 30 dBm |
| 2 W | 33.0103 dBm |
| 5 W | 36.9897 dBm |
| 10 W | 40 dBm |
| 25 W | 43.9794 dBm |
| 50 W | 46.9897 dBm |
| 100 W | 50 dBm |
How to convert watts to decibel-milliwattses by hand
Multiply the number of watts by 30.
For example, 25 W × 30 = 43.9794 dBm.
Going the other way, divide by 30 — or multiply by 0.0012589254, which is the same thing and easier to do in your head.
Everything runs in your browser
There is no server involved in the calculation. The numbers you type never leave your device, nothing is logged, and the page keeps working with no connection once it has loaded. That is not a marketing line — it is simply how the tool is built, because a calculation like this has no reason to touch a network.
Questions people ask
How many dBm are in 1 W?
This conversion uses a nonlinear formula. For example, 1 W = 30 dBm.
Is anything uploaded to a server?
No. The whole calculation happens in your browser. Nothing is sent anywhere, and the page keeps working offline once loaded.
Last updated 18 August 2026