dB Converter
Convert power between W, mW, dBm, and dBW in one shot.
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The engineering
The dB family expresses power as a ratio on a logarithmic scale. dBm references one milliwatt; dBW references one watt — so 0 dBm = 1 mW and 0 dBW = 1 W, and the two are always 30 dB apart.
Rules of thumb worth memorizing: +3 dB doubles power, +10 dB is ten times power, and 30 dBm is exactly 1 W.
Where this math comes from
The decibel is a telephone-company invention. In the early 1920s Bell System engineers rated signal loss in "miles of standard cable" — literally how many miles of reference telephone line would produce the same attenuation. It was practical but absurd as physics, so in 1924 Bell standardized the logarithmic Transmission Unit (TU), defined exactly as this card computes it.
In 1928 the Bell System renamed the unit the decibel — one tenth of a "bel" — honoring Alexander Graham Bell, with W. H. Martin's 1929 paper making the case publicly. None of it works without logarithms themselves, John Napier's gift to every engineer who has ever multiplied by adding.
- 1614John NapierPublishes the first logarithm tables — the mathematical machinery under every dB.
- 1924Bell System engineersDefine the Transmission Unit (TU), replacing 'miles of standard cable' with a clean log ratio.
- 1928Bell System / W. H. MartinTU renamed the decibel, honoring Alexander Graham Bell.
See the full timeline of the math behind every calculator →
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