mW to dBm Calculator
Convert power between milliwatts and dBm, see the formula worked through with your numbers, and look up common values from 0 to 43 dBm.
How to use this tool controls and what to look for
Type a value into any one box and the other two update, or tap one of the quick values from −90 to 30 dBm. The formula below works through your own numbers.
Controls to change
- Power in dBm: enter a dBm value, for example 20 dBm, a typical AP transmit power.
- Power in milliwatts: enter milliwatts, including tiny received values such as 0.000001.
- Power in watts: enter watts, for example 1 W for a high-power radio.
What to look for
- Every +3 dB doubles the power and every +10 dB multiplies it by ten: 20 dBm = 100 mW, 23 dBm ≈ 200 mW, 30 dBm = 1 W.
- A received signal of −67 dBm is about 0.0000002 mW, which is why receivers are measured in dBm, not milliwatts.
- 0 dBm is 1 mW. Negative dBm simply means less than 1 mW, not negative power.
About this tool
Wi-Fi measures power in dBm: decibels relative to one milliwatt. This calculator converts between milliwatts and dBm in either direction, shows the formula with your numbers, and lists common values from typical transmit powers down to the weak signals a device receives.
What you'll learn
- The formulas: dBm = 10 × log10(mW) and mW = 10^(dBm ÷ 10)
- The rules of thumb: +3 dB doubles the power, +10 dB multiplies it by ten
- The difference between dBm, dB and dBi
- Why received Wi-Fi signals, far below a millionth of a milliwatt, are easier to handle in dBm
Common questions
What is 20 dBm in mW?
100 mW. 0 dBm is 1 mW, 10 dBm is 10 mW and 30 dBm is 1 W.
What is a good Wi-Fi signal in dBm?
A common design target is −67 dBm or stronger for voice and video. Data still works at weaker levels, but rates drop quickly below about −75 dBm.
What's the difference between dBm and dB?
dBm is an absolute power level, relative to 1 mW. dB is a ratio, such as a gain or a loss: adding a 5 dB gain to 15 dBm gives 20 dBm.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.