When to use this calculator
Express a power ratio as a decibel difference. Use a dimensionless ratio of powers referenced consistently.
Explore the ac power & reactance calculators for other questions in this topic. For a related calculation, use the Decibel Voltage Ratio Calculator: Express a voltage amplitude ratio as a decibel difference.
PUTTING IT INTO PRACTICE
Decibel Power 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 power ratio | 100 |
| Result | 20 dB |
- Check the input labels and enter the example values above.
- Apply the relationship: Power level difference = 10 log₁₀(power ratio).
- The result is 20 dB, rounded for display.
How to interpret your result
Use a dimensionless ratio of powers referenced consistently.
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 power ratio calculator useful?
Express a power ratio as a decibel difference. Use a dimensionless ratio of powers referenced consistently.
How do I use the decibel power ratio calculator?
Enter positive power ratio. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Power level difference = 10 log₁₀(power ratio).
What should I check before using the result?
Use a dimensionless ratio of powers referenced consistently.
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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