The abundances of the elements in the solar system are usually estimated relative to the abundance of silicon. Since abundances vary widely, a logarithmic scale is used. We report here

(number of atoms of the element in the solar system)
log ----------------------------------------------------------------------
(number of silicon atoms in the solar system / 1 E6 )

Thus the relative solar system abundance of silicon would be log (1 E6) = 6.

Values were obtained from "Abundances of the Elements: Meteoric and Solar ", by E. Anders and N. Grevesse, in Geochimica et Cosmochimica Acta, Vol. 53, pp. 197-214 (1989).