About this tool
Decibel Gain / Ratio Calculator is a free, in-browser tool for working with dB. Choose whether your quantity is a power or a voltage/amplitude, then either enter two values to get the gain in dB, convert a linear ratio to dB, or convert a dB figure back to a linear ratio. It also labels the result as gain, loss or unity. All math is local; nothing is uploaded.
For power, gain in dB = 10 · log₁₀(P2 ⁄ P1) and the ratio back is 10^(dB ⁄ 10). For voltage or amplitude the factor is 20 instead of 10: dB = 20 · log₁₀(V2 ⁄ V1) and ratio = 10^(dB ⁄ 20). The factor of 20 appears because power is proportional to voltage squared, so a voltage ratio contributes twice as many decibels as the same numeric power ratio.
Use it to express an amplifier's gain, an attenuator's loss, or a signal-to-noise improvement in decibels — or to turn a spec sheet's dB figure into a plain multiplier. The decibel here is dimensionless, a ratio between two like quantities.