dB to Voltage Converter
A level of 20 dBV is 10 volts, and the pro audio level of +4 dBu is about 1.23 volts.
Quick answer: Divide the dB by 20, raise 10 to that power, then multiply by the reference voltage. For example, 20 dBV is 10 V, 4 dBu is 1.228 V and 40 dBmV is 0.1 V.
The dB to voltage formula
Voltage equals the reference voltage times 10 to the power of dB divided by 20.
The reference is 1 V for dBV, 0.7746 V for dBu, 1 mV for dBmV and 1 uV for dBuV.
Take 20 dBV. 1 V × 10^(20 ÷ 20) gives 10 V.
Take 4 dBu. 0.7746 V × 10^(4 ÷ 20) gives 1.228 V.
Why voltage uses 20
Power goes with the square of the voltage, so a voltage level uses 20 times the log instead of 10 times (Wikipedia: Decibel).
That is why 6 dB is about double the voltage but about four times the power.
How to convert dB to voltage step by step
- Read the level in dB and the reference, such as dBV or dBu.
- Divide the dB by 20.
- Raise 10 to that power.
- Multiply by the reference voltage to get volts, or by 1,000 for millivolts.
Example 1: 20 dBV
- Start with 20 dBV.
- 1 V × 10^(20 ÷ 20) = 10.
- The voltage is 10 V.
20 dBV = 10 V
Example 2: 4 dBu
- Start with 4 dBu.
- 0.7746 V × 10^(4 ÷ 20) = 1.228.
- The voltage is 1.228 V.
4 dBu = 1.228 V
Example 3: 40 dBmV
- Start with 40 dBmV.
- 1 mV × 10^(40 ÷ 20) = 0.1.
- The voltage is 0.1 V.
40 dBmV = 0.1 V
The three examples below use common sizes.
Each one shows the sum in full.
dB to voltage conversion table
| Level | Voltage (V) | Voltage (mV) |
|---|---|---|
| -10 dBV | 0.3162 V | 316.23 mV |
| 0 dBV | 1 V | 1,000 mV |
| 6 dBV | 1.995 V | 1,995.26 mV |
| 20 dBV | 10 V | 10,000 mV |
| 0 dBu | 0.7746 V | 774.6 mV |
| 4 dBu | 1.228 V | 1,227.65 mV |
| -10 dBu | 0.2449 V | 244.95 mV |
| 20 dBu | 7.746 V | 7,745.97 mV |
| 20 dBmV | 0.01 V | 10 mV |
| 40 dBmV | 0.1 V | 100 mV |
| 40 dBuV | 0.0001 V | 0.1 mV |
| 60 dBuV | 0.001 V | 1 mV |
The highlighted row is the default of the calculator. The last column gives mV.
A quick mental shortcut for dB to voltage
Every 20 dB is a factor of 10 in voltage, and every 6 dB is about a factor of 2.
So 26 dBV is about 20 volts, because 20 dBV is 10 volts and 6 dB doubles it.
Picking the reference
dBV is referenced to 1 volt RMS. dBu is referenced to the voltage that gives 1 milliwatt in 600 ohms, about 0.775 V (Wikipedia: Decibel).
dBmV is referenced to 1 mV across 75 ohms and is common in cable TV, and dBuV is referenced to 1 uV, so 60 dBuV equals 0 dBmV.
Pro and consumer audio levels
Professional line level is plus 4 dBu, about 1.23 V RMS. Consumer line level is minus 10 dBV, about 0.316 V RMS (STX Wiki: Commonly used Voltage and Audio Levels).
Plugging a professional output into a consumer input can overload it.
RMS voltage
The result is an RMS voltage. The peak of a sine wave is about 1.414 times higher.
Keep to RMS when you compare levels.
Quick conversion answers
| Conversion | Result |
|---|---|
| 20 dBV | 10 V |
| 4 dBu | 1.228 V |
| -10 dBV | 0.3162 V |
| 40 dBmV | 0.1 V |
Where this conversion is used
Audio engineers turn a console level in dBu into volts when they match gear.
RF and cable TV technicians read signal levels in dBmV and dBuV.
Common mistakes to avoid
- Using 10 instead of 20. Voltage uses 20 log.
- Mixing dBV and dBu. The two references differ by about 2.2 dB.
- Forgetting the reference. A bare dB value is a ratio, not a voltage.
- Comparing RMS with peak values. Convert both to the same kind first.
Related converters
More voltage levels
-20 dBV is 0.1 V. -6 dBV is 0.5012 V. 3 dBV is 1.413 V.
12 dBV is 3.981 V. 8 dBu is 1.946 V. -20 dBu is 0.07746 V.
60 dBmV is 1 V. 20 dBuV is 0.00001 V. 80 dBuV is 0.01 V.
Doubling the first number
-40 dBV is 0.01 V. -12 dBV is 0.2512 V. 6 dBV is 1.995 V.
24 dBV is 15.85 V. 16 dBu is 4.887 V. -40 dBu is 0.007746 V.
120 dBmV is 1,000 V. 40 dBuV is 0.0001 V. 160 dBuV is 100 V.
The same level on different references
20 dBV is 10 V. 20 dBu is 7.746 V. 20 dBmV is 0.01 V.
20 dBuV is 0.00001 V.
More worked examples
6 dBV is about 1.995 V, and minus 6 dBV is about 0.501 V. 40 dBV is exactly 100 V.
0 dBu is 0.7746 V, 8 dBu is about 1.946 V and 20 dBu is about 7.746 V.
Going from volts to dB
Take 20 times the log of the voltage over the reference. So 2 V is about 6.02 dBV and 0.1 V is exactly minus 20 dBV.
A voltage of 1.228 V is about 4 dBu.
Linking dBV and dBu
A level of 0 dBV is 1 V, and 1 V is about 2.2 dB above the dBu reference of 0.7746 V. So add about 2.2 to a dBV number to get dBu.
So minus 10 dBV is about minus 7.8 dBu, which matches the consumer line level.
Frequently asked questions
How do I convert dB to voltage?
Divide the dB by 20, raise 10 to that power, and multiply by the reference voltage.
How many volts is 20 dBV?
10 volts.
How many volts is 0 dBu?
About 0.7746 volts RMS.
What is plus 4 dBu in volts?
About 1.228 volts RMS.
Why is dBu 0.7746 volts?
It is the voltage that gives 1 milliwatt in 600 ohms.
How much voltage does 6 dB add?
About double. It is a factor of 1.995.
Sources
- Wikipedia: Decibel (en.wikipedia.org)
- STX Wiki: Commonly used Voltage and Audio Levels (projects.ari.oeaw.ac.at)
