The average density of Earth is 5.44 g/cm³.
Mass
Mass = 5.974 × 10²⁴ kg = 5.974 × 10²⁷ g
Volume
d = 2r = 1.28 × 10⁴ km
r = 6.40 × 10³ km × (10³m/1 km) × (10² cm/1 m) = 6.40 × 10⁸ cm
V = ⁴/₃πr³ = ⁴/₃π × (6.40 × 10⁸ cm)³ = 1.098 × 10²⁷ cm³
Density
Density = mass/volume = (5.974 × 10²⁷ g)/(1.098 × 10²⁷ cm³) = 5.44 g/cm³