One sone is defined as the loudness of a 1,000-hertz tone at 40 decibels. This starting point serves as a reference for all other measurements on the scale.

Because the scale is linear, you don't need a degree in acoustics to compare products. If Fan A is rated at 2.0 sones and Fan B is rated at 4.0 sones, you know immediately that Fan B is twice as loud.