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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.

Relative dB (Ratio)
Absolute Power (dBm / mW / W / Vrms)
Power in dBW—
💡 Usage & Formula

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 use 20·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.
📖 References: Decibel (Wikipedia)