What is the name of the scale used to measure earthquakes?

Earthquakes are measured with the Richter Magnitude Scale developed by Charles F. Richter of California Institute of Technology in 1935. Here is a summary of the Richter scale:
Magnitude less than 3.5: Generally not felt, but recorded.
Magnitude 3.5-5.4: Often felt, but rarely causes damage.
Magnitude under 6.0: At most slight damage to well-designed buildings over small regions.
Magnitude 6.1-6.9: Can be destructive in areas up to 100 kilometers across where people live.
Magnitude 7.0-7.9: Major earthquake. Can cause serious damage over larger areas.
Magnitude 8 or greater: Great earthquake. Can cause serious damage in areas several hundred kilometers across.
Earthquakes are also measured by the Mercalli Intensity Scale which is a longer, more detailed scale. Both the Richter Scale and the Mercalli Scale can be seen on the U.S. Geological Survey website.

Source: United States Geological Survey.