Subtract the radius (r) from the total length (l) two times since there is one corner on each end. The result is the length of the un-rounded portion of the side (s).
Subtract r from the total width two times to find the length of the un-rounded portion of the end (e).
Calculate the perimeter of the corners according to circumference formula C = 2 * pi * r. Since there are four quarter circles, one at each corner, the total perimeter of the corners is equal to the perimeter of a full circle.
Calculate the total perimeter according to the formula P = C + (2 * s) + (2 * e). C represents the total perimeter of all four corners. (2 * s) is the total length of the two un-rounded portions of the long sides of the rink and (2 * e) is the total length of the two un-rounded parts of the ends.