Electrical and electronics
Decibel calculator: dB, dBm, dBW, dBV, dBu and ratios
Convert between decibels and power or amplitude ratios, and between dBm, dBW, watts, volts, dBV, dBu and dBµV at a chosen impedance.
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Result
- Power and voltage are related through the impedance: P = V² / R with R = 50 Ω. dBV, dBu and dBµV are voltage levels and do not depend on impedance; dBm and dBW are power levels.
Method and limits
A decibel value expresses a power ratio as 10 log10(P2/P1), or a ratio of field quantities (voltage, current, sound pressure) in the same impedance as 20 log10(V2/V1); both give the same dB for the same physical change. Absolute levels fix the reference: dBm is relative to 1 mW, dBW to 1 W, dBV to 1 V, dBu to 0.7746 V (the voltage that puts 1 mW into 600 Ω) and dBµV to 1 µV. Power and voltage levels are linked by P = V² / R at the stated impedance.
Worked examples: 0 dBm in 50 Ω is 1 mW and 0.2236 V RMS, which is −13.01 dBV, −10.79 dBu and 106.99 dBµV; 30 dBm = 1 W = 0 dBW; +3 dB is a power ratio of 1.995 and an amplitude ratio of 1.413.
Limits
RMS values of steady signals are assumed; peak and peak-to-peak voltages are shown for a sine wave only. Acoustic levels (dB SPL, dBA) use other references and weightings and are not covered.
References
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