According to Wikipedia, “[t]he decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity, often power or intensity.” We usually hear it applied to sound. It is also applied to radio communications. For instance, your phone usually has a setting that gives the signal strength in decibels.

In practice, this means there needs to be two measured values in order to have a ratio. The numerator of the ratio is the measured value. The denominator is a reference value, a standard number we already know. For measuring sound this [latex]p_0[/latex], or the pressure at 20 micropascals in air. So when measuring sound,

But this definition implies I could apply it to any other physical quantities provided the base units were the same. So, being ridiculous, and using Earth as a reference value, we know the mass of Jupiter is,

Neat.

*Image by Kevin Gill / Flickr.*