The carpet is held by the plastic rivets. Here are the measurements, they are the best i could get, but, the carpet bends with the contour of the trunk straight down the middle, and the edges are all curved so these measurements are measured from the WIDEST corners of the area.
ACROSS
Top: 32 5/8"
Middle: 39"
Bottom: 41"
DIAGONAL
Top Left to bottom right: 40"
Top Right to bottom left: 40"
Top to Bottom:
Left: 19 5/8"
Middle: 18 6/8"
Right: 19 5/8"
These measurements are about 99% accurate, like i said before it was diffcult to measure them precisely b/c of the bending of the carpet and the rounded edges.