dB Calculator
Convert between decibels, power ratios, and voltage ratios for RF and audio applications.
Common: 1W, 1mW (for dBm), 1kW
Enter values to see results
Common dB Values Reference
| 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 |
Power Decibels
dB = 10 × log₁₀(P₂/P₁)
P₂/P₁ = 10^(dB/10)
Used for power measurements: RF power, audio power, signal strength
Voltage Decibels
dB = 20 × log₁₀(V₂/V₁)
V₂/V₁ = 10^(dB/20)
Used for voltage/amplitude: audio levels, sensor signals, gain
Understanding Decibels
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.
Why Logarithmic?
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 vs Voltage
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.
Common dB Scales
dBm (Milliwatt)
Power referenced to 1 milliwatt. Used in RF and telecommunications.
- • 0 dBm = 1 mW
- • +30 dBm = 1 W
- • -30 dBm = 1 µW
dBW (Watt)
Power referenced to 1 watt. Common in high-power RF systems.
- • 0 dBW = 1 W
- • +30 dBW = 1 kW
- • dBW = dBm - 30
dBu (Audio)
Voltage referenced to 0.775V (1mW into 600Ω). Professional audio standard.
- • 0 dBu = 0.775 V
- • +4 dBu = 1.228 V (pro line level)
- • -10 dBV ≈ -7.8 dBu
dBV (Volt)
Voltage referenced to 1 volt RMS. Used in consumer audio.
- • 0 dBV = 1 V
- • -10 dBV = 0.316 V (consumer line)
- • dBV = dBu - 2.2
dBµV (Microvolt)
Voltage referenced to 1 microvolt. EMC and antenna measurements.
- • 0 dBµV = 1 µV
- • 60 dBµV = 1 mV
- • 120 dBµV = 1 V
dBi / dBd (Antenna)
Antenna gain relative to isotropic (i) or dipole (d) reference.
- • dBi = gain vs isotropic
- • dBd = gain vs dipole
- • dBi = dBd + 2.15
Practical Applications
Link Budget Calculation
RF engineers use dB to calculate signal strength through a wireless link:
All values in dB simply add/subtract instead of multiply/divide.
Audio Gain Staging
Audio engineers chain gain stages using dB:
Keep signal-to-noise ratio high by proper gain staging.