How to Use
- Enter values
Input the power, voltage, or noise level value you want to convert.
- Select unit
Choose the desired decibel unit such as dB, dBm, or dBW.
- View results
Click Calculate to see the converted decibel value and ratio.
What Is a Decibel (dB)?
The decibel (dB) is a dimensionless unit that expresses the ratio between two physical quantities on a base-10 logarithmic scale. It equals one tenth of a bel (B) and is widely used in acoustics because human hearing perceives the intensity of a stimulus logarithmically.
The key idea behind the decibel is that it represents a ratio relative to a reference, not an absolute value. The same 60 dB can mean very different things depending on the reference you choose. Logarithms are used because the quantities being measured span an enormous range. Audible sound pressure, for example, differs by more than a trillion times in energy between the faintest sound and the threshold of pain, yet a logarithmic transform compresses this into a manageable 0-120 dB range.
This calculator supports two modes: power ratio and voltage ratio. You can use it for acoustic measurements, audio signal gain, and calculating losses in antennas and communication lines.
Calculation Formula
When working with a ratio of power (or acoustic energy), use dB = 10 × log₁₀(P1 / P2). For amplitude-type quantities such as voltage, current, or sound pressure, power is proportional to their square (P ∝ V²), so you use dB = 20 × log₁₀(V1 / V2).
Variable meaning: P1 and V1 are the measured values; P2 and V2 are the reference values.
Example 1 (power ratio): With an output of 100 W and a reference of 1 W, dB = 10 × log₁₀(100 / 1) = 10 × log₁₀(100) = 10 × 2 = 20 dB.
Example 2 (voltage ratio): With a 2 V signal and a 1 V reference, dB = 20 × log₁₀(2 / 1) = 20 × 0.301 ≈ 6.02 dB. In other words, doubling the voltage adds about 6 dB.