Standard Size:  175 X 180 X 40 [20 X 60] [170 X 60 X 10] mm  [(L * W* H) (b*d) (l1*w1*w2)] mm in which L = Length; W = Width; H= Height; b=base length; d= depth; l1 = inner length; w1 = median width; w2 = edge width  in milimeters. 
It looks like heart shaped with elevated areas to protect heel on either side. Inner curvature provide padded platform for the heels during prolonged surgeries
Ergonomically designed to relieve pressure, enhanced blood flow to extremities with padded support till ankle region.