 The cuboid's face diagonals can have up to three different lengths, since the faces come in congruent pairs and the two diagonals on any face are equal.The cuboid's space diagonals all have the same length.If the edge lengths of a cuboid are "a", "b", and "c", then the distinct rectangular faces have edges ("a", "b"), ("a", "c"), and ("b", "c"); so the respective face diagonals have lengths formula_1 formula_2 and formula_3

Thus each face diagonal of a cube with side length "a" is formula_4.