The absolute value of the static quadrupole moment Q(21+) expressed by B(E2) values

A simple parameter-free formula is derived within the IBA which expresses the absolute value of the quadrupole moment of the first 2+ state in terms of four E2-transition probabilities connecting low-lying collective states. A comparison with IBA-1 calculations shows that in realistic cases the formula is nearly exact. Comparisons to experiment are given for several nuclei associated with different regions of the symmetry triangle.