Audio calculator
dBu / dBV / Volts Converter
dBu is decibels relative to 0.7746 volts RMS and dBV is decibels relative to 1 volt RMS, so the two scales sit a constant 2.22 dB apart: 0 dBV equals +2.22 dBu. Enter a level in any unit and this converter returns all the others, plus power into a chosen load.
600 ohms is the legacy line termination; modern line inputs are bridging (10k+) and transfer voltage, not power.
Formulas
dBu from voltage
dBu = 20 × log10(V / 0.7746)- V:
- signal voltage in volts RMS
- 0.7746:
- the voltage that dissipates 1 mW in 600 ohms (√0.6)
dBV from voltage
dBV = 20 × log10(V / 1.0)- V:
- signal voltage in volts RMS
Power into a load
P = V² / R- P:
- power in watts
- R:
- load impedance in ohms
How it works
The 0.7746 V reference is a fossil from telephone practice: it is the voltage that delivers exactly 1 milliwatt into a 600 ohm line. When audio moved to bridging inputs that measure voltage rather than transfer power, the reference voltage survived as dBu ("u" for unloaded). dBV simply uses a cleaner 1 volt reference.
The two scales never drift apart: dBu = dBV + 2.218. That is why professional +4 dBu equipment and consumer -10 dBV equipment differ by about 11.8 dB of signal level, not the 14 dB the raw numbers suggest.
Interfacing the two worlds is a gain-structure problem: a -10 dBV consumer output feeding a +4 dBu input needs roughly 12 dB of make-up gain somewhere, and a +4 dBu output into consumer gear will clip it unless padded down.
Worked example: What voltage is a +4 dBu line-level signal?
- 1.V = 0.7746 × 10^(4/20) = 0.7746 × 1.585 = 1.228 V RMS.
- 2.In dBV: 20 × log10(1.228) = +1.78 dBV, which is +4 minus the 2.22 dB offset.
- 3.Into a legacy 600 ohm termination: P = 1.228² / 600 = 2.51 mW.
+4 dBu is 1.228 V RMS, or +1.78 dBV.
Common operating levels
| Level | dBu | dBV | Volts RMS |
|---|---|---|---|
| Professional line nominal | +4 dBu | +1.78 dBV | 1.228 V |
| Consumer line nominal | -7.78 dBu | -10 dBV | 0.316 V |
| Typical mic level (speech, dynamic) | -50 dBu | -52.2 dBV | 2.45 mV |
| 0 dBV reference | +2.22 dBu | 0 dBV | 1.000 V |
| Typical console max output | +24 dBu | +21.8 dBV | 12.28 V |
Field notes
- Console meters usually read dBu or dBFS, not dBV. Check which before chasing a 2 dB "discrepancy" that is just the unit offset.
- A DI box or an interface pad, not the fader, is the right place to absorb the consumer/pro level gap when a laptop feeds the PA.
Frequently asked questions
What is the difference between dBu and dBV?
Only the reference voltage. dBu references 0.7746 V RMS, dBV references 1 V RMS, and any level in dBu is the dBV figure plus 2.218 dB. Neither depends on impedance on modern bridging inputs.
How many dB apart are +4 dBu and -10 dBV?
About 11.8 dB. Convert -10 dBV to dBu (-10 + 2.22 = -7.78 dBu) and the gap to +4 dBu is 11.78 dB, which is the make-up gain needed when consumer gear feeds a professional input.
Is 0 dBu the same as 0 dBm?
Only across a 600 ohm load. dBm is power (1 mW reference); dBu is voltage. The units coincide numerically when the load is exactly 600 ohms, which almost nothing modern is.