When to use this calculator
Express a voltage amplitude ratio as a decibel difference. The 20-log voltage form implies equal impedance when interpreted as a power ratio.
Explore the ac power & reactance calculators for other questions in this topic. For a related calculation, use the Decibels to Power Ratio Calculator: Recover a linear power ratio from a decibel difference.
PUTTING IT INTO PRACTICE
Decibel Voltage Ratio: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Positive voltage ratio | 10 |
| Result | 20 dB |
- Check the input labels and enter the example values above.
- Apply the relationship: Voltage level difference = 20 log₁₀(voltage ratio).
- The result is 20 dB, rounded for display.
How to interpret your result
The 20-log voltage form implies equal impedance when interpreted as a power ratio.
Use RMS values in the AC power relationships. Apparent power is measured in VA and real power in watts. Pure-sine conversions and balanced three-phase equations only apply under their stated assumptions.
Frequently asked questions
Why can volt-amps differ from watts?
Apparent power is the RMS voltage-current product, while real power also reflects power factor. They are numerically equal only at a power factor of one.
When is the decibel voltage ratio calculator useful?
Express a voltage amplitude ratio as a decibel difference. The 20-log voltage form implies equal impedance when interpreted as a power ratio.
How do I use the decibel voltage ratio calculator?
Enter positive voltage ratio. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Voltage level difference = 20 log₁₀(voltage ratio).
What should I check before using the result?
The 20-log voltage form implies equal impedance when interpreted as a power ratio.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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