Calculator Inputs
Formula Used
Equal impedance voltage ratio:
dB = 20 × log10(Vinput / Vreference)
Use this when both measurements share the same impedance conditions.
Power-equivalent comparison when impedances differ:
dB = 10 × log10[(Vinput² / Rinput) / (Vreference² / Rreference)]
This adjusts the result because voltage alone does not fully describe power across different resistances.
How to Use This Calculator
- Enter the measured input voltage and choose its unit.
- Select a preset reference such as dBV, dBu, dBmV, or dBµV.
- Choose custom reference mode when you want your own baseline voltage.
- Enter signal and reference impedances for a power-aware comparison.
- Optionally enter a second voltage to compare two measured levels.
- Press the calculate button to view the decibel result, table, graph, and export options.
Example Data Table
| Input Voltage | Reference | Formula | Result |
|---|---|---|---|
| 0.1 V | 1 V | 20 × log10(0.1 / 1) | -20.00 dBV |
| 0.5 V | 1 V | 20 × log10(0.5 / 1) | -6.02 dBV |
| 0.775 V | 0.775 V | 20 × log10(0.775 / 0.775) | 0.00 dBu |
| 2 V | 1 V | 20 × log10(2 / 1) | 6.02 dBV |
| 2000 µV | 1 µV | 20 × log10(2000 / 1) | 66.02 dBµV |
Frequently Asked Questions
1. How is voltage converted to decibels?
Use 20 times the base-10 logarithm of the voltage ratio. Divide measured voltage by reference voltage, then apply the formula.
2. Why does the calculator use 20 log instead of 10 log?
Voltage is an amplitude quantity. Power is proportional to voltage squared, so amplitude ratios use 20 log while power ratios use 10 log.
3. Can I compare voltages with different impedances?
Yes. The calculator shows a power-equivalent decibel result using both voltage and impedance, which is more accurate when resistances are not equal.
4. What does dBV mean?
dBV means decibels referenced to 1 volt. A reading of 0 dBV equals exactly 1 V RMS.
5. What does dBu mean?
dBu means decibels referenced to 0.775 volts. It is common in professional audio and line-level signal work.
6. Can the result be negative?
Yes. A negative dB value means the input voltage is smaller than the chosen reference voltage.
7. Why must the voltage be greater than zero?
The logarithm of zero or a negative voltage ratio is undefined in this context, so the calculator requires positive values.
8. Which unit should I enter?
Choose the unit that matches your measurement source. The calculator converts kV, V, mV, and µV into volts automatically.