Two things...
First, here's the NCAA Contractual Language for MATS;
"Arrangements to secure eight 42’ x 42’ wrestling mats will be made by the national office with
copies of all correspondence sent to the host institution/conference. The host
institution/conference or sponsoring agency should deal directly with the mat company to
confirm drop-off/pick-up. These mats will be supplied by Resilite, the official NCAA mat company.
The NCAA staff, in consultation with the hosts, will determine the color schematic layout of the
various mats."
Soooo...given the 5' apron requirement, the mats all have a 32' diameter wrestling area.
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Second, here's some history, with credit to Mark Palmer, the author of this info...
Before the mid-1950s, mats usually had a canvas surface, sometimes covered with plastic or rubber, but oftentimes with a fabric such as moleskin or canton flannel which could not be easily wiped clean, and, in fact, might be washed only a couple times a year. As to what was underneath the surface … anything from horsehair to shredded newspapers to straw to wood shavings was the stuff inside mats of the past. These materials did not provide the level of shock absorption -- and safety to wrestlers -- that today's foam-filled mats do.
The dimensions of the wrestling area have also changed over the years. In the 1920s and 30s, the standard mat size was 20-feet square. The NCAA rules published in the 1947 edition of The Official Wrestling Guide stated, "The area of the mat shall not be less than 20 feet by 20 feet, and a 24-foot by 24-foot mat shall be considered standard." Fifteen years later, the 1963 edition of The Official Wrestling Guide had illustrations of minimum mat sizes, including a 34-foot square mat with a 24-foot square wrestling surface marked on it, as well as a round mat with a circular wrestling area of 28 feet in diameter, with a five-foot safety zone extending beyond that. The latest rules mandate a clearly-marked circular wrestling surface of 32-42 feet in diameter, with a minimum of five feet of mat beyond the wrestling surface.
The ring's the thing
Walk into a wrestling meet at Oklahoma State, University of Iowa, University of Northern Iowa, Northwestern or some other colleges back in the 1920s or 30s, and, most likely, at the center of the gym you'd find a roped-off wrestling ring. At some schools -- most notably Oklahoma State -- the ring was raised up off the gym floor, much like we associate with professional wrestling or boxing events today.
Wrestling ring at the University of Northern Iowa (Called Iowa State Teachers College at the time)
The wrestling area inside the ring was the same as on the open mats of other colleges -- 20 feet square, with an apron at the edge of the mat. Rules dictated that there be no less than three parallel ropes on each side of the ring, and that the ring posts be padded and set back from the edge of the corners. Unlike professional wrestling, the ropes could not be used in any way during the match; a wrestler could not gain leverage from the ropes, "rebound" off them, or duck through them to take a break.
According to Cowboys Ride Again! -- Bob and Doris Dellinger's book on the history Oklahoma State's wrestling program -- ropes and rings became illegal in 1942, the last full season of college wrestling before a three-year hiatus for World War II. In the 1947 Official Wrestling Guide, in the rules section titled "Mats, Ropes and Costumes" it states in large, bold type: "Ropes and Raised Platforms are Illegal."
