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dB & dBm Converter
Calculate decibel ratios (power/voltage) and absolute RF power across dBm, mW, W, dBW and Vrms (over a reference impedance, default 50 Ω) — all bidirectional.
Decibels (dB) are logarithmic units expressing ratios of power or voltage. dBm expresses absolute power relative to 1 milliwatt.
Formulas:
- Relative Power:
dB = 10 * log10(P2 / P1) - Relative Voltage:
dB = 20 * log10(V2 / V1) - Absolute Power (dBm):
dBm = 10 * log10(Power_mW / 1mW) - Power (mW):
Power_mW = 10^(dBm / 10) - Watts & dBW:
W = mW / 1000,dBW = dBm − 30 - RMS voltage over impedance R:
P = Vrms² / R→Vrms = √(P · R)(default R = 50 Ω)
Usage: Switch modes and fill in any field. The absolute-power group converts between dBm, mW, W, dBW, and Vrms (across the reference impedance) bidirectionally — enter any one and the rest update.
When you need it: Converting between linear ratios, dB, and absolute dBm power — stacking RF gains and losses, reading a link budget, or translating audio and sensor levels.
Worked example: 0 dBm = 1 mW and +30 dBm = 1 W. A 2× power ratio is +3 dB; a 2× voltage ratio is +6 dB. Feed −10 dBm into a 20 dB amplifier and you get +10 dBm = 10 mW.
Tips & gotchas:
- Power uses
10·log₁₀; voltage, current and field quantities use20·log₁₀— mixing them is the classic error. - dBm is absolute (referenced to 1 mW); plain dB is a relative ratio with no fixed reference.
- +3 dB ≈ double the power, +10 dB = 10× — handy for mental math.
- Add and subtract gains/losses in dB along a chain; never multiply them.