The largest great white shark ever caught actually much larger than 20 feet. According to the Guinness Book of Records, the two largest great white sharks ever found were 36' and 37' respectively, in length. There is some speculation on it, but Guiness is pretty thorough before adding it to their books, they would have come to measure and weigh it, not just taken a random story. Who knows though, it was quite a while ago.

The majority, however, measure between 13 and 16 feet with an average weight of 1,500 to 2,450 pounds.

Width is harder, they can be several feet around....but it depends on the sharks size and weight. Average larger ones can be about 3+ feet wide at the head. Larger of course is more than possible, these animals can live for long periods and grow 1-2 feet a year. Largely theorized they do not stop growing, they just slow down depending on the water and food supply.

The biggest great white sharks can reach up to 20 feet long....