RF · power units
dBm to mW converter.
Type a power in any one unit and read it in dBm, dBW, milliwatts and watts.
Inputs
Power in every unit
Enter values to calculate.
How do I convert dBm to milliwatts?
dBm is power in decibels relative to 1 milliwatt. Power in mW is 10(dBm / 10), and dBm is 10 x log10 (mW). dBW is the same idea relative to 1 watt, so dBm = dBW + 30. Because the scale is logarithmic, every 3 dB roughly doubles the power and every 10 dB multiplies it by 10.
Worked example. 20 dBm is 100 mW, or 0.1 W, or -10 dBW. A weak Wi-Fi signal of -90 dBm is 0.000000001 mW, which is 1 picowatt.
| dBm | mW |
|---|---|
| -30 | 0.001 |
| -10 | 0.1 |
| 0 | 1 |
| 10 | 10 |
| 20 | 100 |
| 30 | 1000 |
| 36 | 3981.1 |
Gains and losses (dB) add to a level in dBm; you never add two dBm values directly, you convert to mW, add, and convert back.
Frequently asked questions
What is 0 dBm in watts?
0 dBm is 1 milliwatt, which is 0.001 W. 30 dBm is exactly 1 W.
How do I convert dBm to dBW?
Subtract 30. 20 dBm is -10 dBW.
Can I add two dBm values?
No. Convert each to milliwatts, add them, then convert back. Two equal signals add 3 dB, not double the dBm number.
Why is Wi-Fi signal strength negative dBm?
Received signals are far below 1 mW, so their dBm values are negative. -50 dBm is stronger than -80 dBm.
Sources
Checked
dBm and dBW are defined as decibels relative to 1 mW and 1 W, so this is arithmetic only. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Power-unit arithmetic. Real transmit power limits are set by the regulator in your country; check them before you transmit.