The May 31, 2013 El Reno tornado was the widest ever recorded at 2.6 miles wide. It’s worth showing how much wider the tornado was than any other EF5 tornado:

Source: AP/ABC News; NWS; CNN

Note: “0.2” represents tornadoes that were 0.01 – 0.20 miles wide, “0.4” represents tornadoes that were 0.21 – 0.40 miles wide, and so forth.  The Moore, OK 2013 tornado was 1.3 miles wide, so it goes in the bin labelled “1.4”.