dBm is power measured against 1 milliwatt: P (mW) = 10^(dBm ÷ 10). 0 dBm is 1 mW, 20 dBm is 100 mW and 30 dBm is 1 W. Every +10 dBm multiplies power by 10 and every +3 dBm roughly doubles it.
dBm is a power scale referenced to 1 milliwatt. 0 dBm is 1 mW, every +10 dBm multiplies power by 10, and every +3 dBm roughly doubles it. Wi-Fi radios, two-way radios and fiber transceivers are rated in dBm. Enter one number to see it in watts.
Result
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Formula
- P (mW) = 10^(dBm ÷ 10)
- dBm = 10 × log10(P ÷ 1 mW)
- dBW = dBm − 30
How to use it
- Choose whether you know dBm, mW, W or dBW.
- Enter the value. dBm and dBW can be negative.
- All four units update together.
This is an estimating tool. Follow your local electrical code and have a qualified electrician confirm any real installation.
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Frequently asked questions
What does dBm mean?
dB expresses a ratio and the m says the reference is 1 milliwatt, so dBm is an absolute power. Wi-Fi, cellular and fiber equipment use it because their power spans microwatts to watts, and a log scale keeps those numbers readable.
What is dBi, and how is it different from dBm?
dBi is antenna gain: how much an antenna concentrates energy in one direction compared with an ideal isotropic antenna. It is not a power. Transmitter power in dBm plus antenna gain in dBi, ignoring cable loss, gives the effective radiated power.
What dBm is a good phone signal?
Closer to zero is stronger. Around −70 dBm or better is generally good, and below about −100 dBm calls and data start to drop, though the exact thresholds depend on the network technology.
How do I convert dBm to dBW?
dBW is referenced to 1 watt, and 1 W is 1000 mW, a 30 dB step. So dBW = dBm − 30.
