Convert between decibels, power ratios, and voltage ratios for RF and audio applications.
Common: 1W, 1mW (for dBm), 1kW
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| dB | Power Ratio | Voltage Ratio | Description |
|---|---|---|---|
| +40 dB | 10,000× | 100× | Very high gain |
| +20 dB | 100× | 10× | High gain amplifier |
| +10 dB | 10× | 3.16× | Moderate gain |
| +6 dB | 4× | 2× | Double voltage |
| +3 dB | 2× | 1.41× | Double power |
| 0 dB | 1× | 1× | Unity / Reference |
| -3 dB | 0.5× | 0.71× | Half power (cutoff) |
| -6 dB | 0.25× | 0.5× | Half voltage |
| -10 dB | 0.1× | 0.316× | One-tenth power |
| -20 dB | 0.01× | 0.1× | One-tenth voltage |
dB = 10 × log₁₀(P₂/P₁)
P₂/P₁ = 10^(dB/10)
Used for power measurements: RF power, audio power, signal strength
dB = 20 × log₁₀(V₂/V₁)
V₂/V₁ = 10^(dB/20)
Used for voltage/amplitude: audio levels, sensor signals, gain
The decibel (dB) is a logarithmic unit used to express ratios of power or amplitude. Because it's logarithmic, it compresses large ranges into manageable numbers and simplifies multiplication to addition.
Human perception of sound and light is roughly logarithmic. A signal that's 10× more powerful sounds only about twice as loud. Decibels match this perception and make calculations easier.
Power uses 10×log₁₀ because P ∝ V². Voltage uses 20×log₁₀ to maintain consistency. A 6 dB increase means 4× power but only 2× voltage.
Power referenced to 1 milliwatt. Used in RF and telecommunications.
Power referenced to 1 watt. Common in high-power RF systems.
Voltage referenced to 0.775V (1mW into 600Ω). Professional audio standard.
Voltage referenced to 1 volt RMS. Used in consumer audio.
Voltage referenced to 1 microvolt. EMC and antenna measurements.
Antenna gain relative to isotropic (i) or dipole (d) reference.
RF engineers use dB to calculate signal strength through a wireless link:
All values in dB simply add/subtract instead of multiply/divide.
Audio engineers chain gain stages using dB:
Keep signal-to-noise ratio high by proper gain staging.