Calculator inputs
Use the responsive form below. It shows three columns on large screens, two on smaller screens, and one on mobile.
Formula used
Power ratio conversion: dB = 10 × log10(P2 / P1)
Amplitude ratio conversion: dB = 20 × log10(A2 / A1)
Fraction input: ratio = numerator / denominator, then apply the appropriate decibel formula.
Use the amplitude equation only when the compared amplitudes share the same impedance. If impedance changes, compare power instead.
How to use this calculator
- Select Power ratio or Amplitude ratio.
- Choose Direct ratio or Numerator / denominator.
- Enter the required values and set your preferred decimal precision.
- Click Convert ratio to dB.
- Review the result card, worked formula, and Plotly graph above the form.
- Use the CSV or PDF buttons to download your result report.
Example data table
| Case | Type | Linear Ratio | Decibel Result | Meaning |
|---|---|---|---|---|
| Example 1 | Power | 2.0 | 3.0103 dB | Power doubles relative to the reference. |
| Example 2 | Power | 0.5 | -3.0103 dB | Power halves relative to the reference. |
| Example 3 | Amplitude | 2.0 | 6.0206 dB | Amplitude doubles under equal impedance. |
| Example 4 | Amplitude | 10.0 | 20.0000 dB | Amplitude is ten times the reference. |
| Example 5 | Power | 10.0 | 10.0000 dB | Power is ten times the reference. |
| Example 6 | Amplitude | 0.5 | -6.0206 dB | Amplitude drops to half the reference. |
Frequently asked questions
1) What does a positive dB result mean?
A positive decibel value means the measured quantity is larger than the reference. Higher positive values represent stronger gain or larger ratios.
2) What does a negative dB result mean?
A negative result means the measured quantity is smaller than the reference. It indicates loss, attenuation, or reduction from the baseline value.
3) When should I use the power formula?
Use the power equation when you are comparing watts, milliwatts, energy flow, intensity, or any quantity directly proportional to power.
4) When should I use the amplitude formula?
Use the amplitude equation for voltage, current, pressure, or field quantities only when both measurements share the same impedance conditions.
5) Why does doubling power give about 3 dB?
Because 10 × log10(2) equals 3.0103. That is why a doubled power ratio is commonly approximated as a 3 dB increase.
6) Why does doubling amplitude give about 6 dB?
Because 20 × log10(2) equals 6.0206. Amplitude quantities use the factor 20, so doubling creates a larger decibel shift.
7) Can I enter values smaller than one?
Yes. Ratios between zero and one are valid and will produce negative decibel results, showing attenuation relative to the reference.
8) What does 0 dB mean?
A 0 dB result means the ratio equals exactly one. The measured quantity and the reference quantity are the same.