From the conversion of units: 1 cm^3 is equivalent to 1 mL 1 L is equivalent to 1000 mL therefore, to convert from liter to cm^3, we simply multiply by 1000. Note that the multiplication will be done in the denominator.
Based on this: density = (0.625 g/l) x (1g/1000 cm^3) = 0.000625 g/cm^3 = 6.25 x 10^-4 g/cm^3
