How are tornados rated?

Fujita Scale F0 to 5: Tornado intensities are classified on the Fujita Scale with ratings between F0 (weakest) to F5 (strongest). Although severe tornadoes are more common in the Plains States, tornadoes have been reported in every state.

Rated 0-5: Tornadoes are among the most dangerous storms on Earth and, as meteorologists strive to protect vulnerable populations through early warning, it helps to classify storms by severity and potential damage. http://science.howstuffworks.com/nature/climate-weather/storms/tornado3.htm