Decibels (dB) are not units of measure like feet, inches, and pounds. Decibel is a comparison between two values and is a common expression of electrical and acoustic measurements. Decibel is a number that represents the ratio of two quantity values (such as voltage). It is actually a logarithmic ratio and is intended to reduce the larger metric range to a smaller, more user-friendly range. The decibel relation formula for voltage is: dB = 20 x log(V1/V2).