dB Converter
Convert between decibels and voltage / power ratios in both directions.
Enter dB value
dB
Common values
Results
dB (voltage ref)— dB
dB (power ref)— dB
Voltage ratio— ×
Power ratio— ×
% of input (V)—
Formulas
dB (voltage ref)
dB = 20 · log₁₀(Vout / Vin)dB (power ref)
dB = 10 · log₁₀(Pout / Pin)Ratio from dB
ratio = 10^(dB/20) [voltage]Understanding decibels
The decibel is a logarithmic unit used to express ratios of power or amplitude. Because power is proportional to the square of voltage, voltage ratios use a factor of 20 while power ratios use a factor of 10.
Key Reference Points
- −3 dB ≈ half power, 70.7% of voltage
- −6 dB ≈ half voltage, 25% of power
- −20 dB = ÷10 voltage, ÷100 power
- +6 dB ≈ ×2 voltage, ×4 power
- +20 dB = ×10 voltage, ×100 power
- 0 dB = unity (no gain or loss)