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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A place to ask real electricians your questions is still being planned. We will decide whether to build it once we see how many people need it. There is no launch date yet, and we are not collecting any contact details here. Your click has been counted.
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.
