Comparing Decibels to Voltage, Power, and Loudness

Although loudness is for the most part subjective, it is often quantified using dB-SPL. Decibels (dB) are the logarithm of the ratio of a measured value to a reference value. For dB-SPL, the reference value is the threshold of human hearing. However, decibels are also used to measure other values, such as voltage (V) and power (watts). Because these values are logarithmic, they can be a somewhat confusing. For example, doubling the wattage of an amplifier output does not equal twice the volume. The chart below will help show the relationship of these various units.