Charles Richter introduced the Richter scale in 1935 to measure earthquake size.
Richter developed the scale with Beno Gutenberg at the California Institute of Technology. It was designed for earthquakes in Southern California and used the logarithm of the largest seismic-wave amplitude recorded by a particular type of seismograph, adjusted for distance from the epicenter.
Because the scale is logarithmic, an increase of one magnitude represents ten times the recorded wave amplitude. It also corresponds to roughly 31.6 times more energy released. The scale is often called the local-magnitude scale, or ML.
A common mix-up is treating Richter magnitude and earthquake intensity as the same thing. Magnitude describes the earthquake's overall size, while intensity describes shaking and damage at particular locations. Modern seismologists usually prefer the moment magnitude scale for very large earthquakes because it remains reliable across a wider range of sizes.