How big can a tornado get?

It is unknown how large and strong a tornado can get. As of 2013, the strongest wind speed recorded in a tornado was 318 mph in 1999 Moore, Oklahoma, by Doppler on Wheels (DOW), and the widest tornado on record occurred on May 31, 2013, near El Reno, Oklahoma.

The El Reno tornado was estimated to be 2.6 miles wide at one point, breaking the 2004 record of 2.5 miles in Hallam, Nebraska. DOW has only recorded less than 0.1 percent of winds created by tornadoes, leaving thousands more throughout history undocumented, so it's unknown whether stronger tornadoes have been unrecorded.