Logarithmic scale

A logarithmic scale is a nonlinear scale used when there is a large range of quantities. Common uses include the earthquake strength, sound loudness, light intensity, and pH of solutions.

It is based on orders of magnitude, rather than a standard linear scale, so each mark on the scale is the previous mark multiplied by a value.

Common usages

The following are examples of commonly used logarithmic scales, where a larger quantity results in a higher value:

  • Richter magnitude scale and moment magnitude scale (MMS) for strength of earthquakes and movement in the earth.
  • bel and decibel and neper for acoustic power (loudness) and electric power;
  • cent, minor second, major second, and octave for the relative pitch of notes in music;
  • logit for odds in statistics;
  • Palermo Technical Impact Hazard Scale;
  • logarithmic timeline;
  • counting f-stops for ratios of photographic exposure;
  • rating low probabilities by the number of 'nines' in the decimal expansion of the probability of their not happening: for example, a system which will fail with a probability of 10−5 is 99.999% reliable: "five nines".
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    Scientists will try to deacidify a tiny patch of the Gulf of Maine

    Bangor Daily News 10 Mar 2025
    While today’s ocean water remains basic, the pH scale is logarithmic and the drop of 0.1 units translates to about a 30 percent increase in acidity.
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