A remarkable formula for the asymptotic behavior of the 6- j symbol was first conjectured by Ponzano and Regge and later proven by Roberts. The asymptotic formula applies when all six quantum numbers j 1,..., j 6 are taken to be large and associates to the 6- j symbol the geometry of a tetrahedron. If the 6- j symbol is determined by the quantum numbers j 1,..., j 6 the associated tetrahedron has edge lengths J i = j i +1/2 (i=1,...,6) and the asymptotic formula is given by,