Original:  If only the Earth's land area of 150,000,000km2 (58,000,000 sq. mi.) is taken into account, then human population density is 50 per km2 (129 per sq. mi.).
Revised:  However, if only the Earth's land area of 150,000,000km2 (58,000,000 sq. mi.) is taken into account, then human population density is 50 per km2 (129 per sq. mi.).
Edit intent: coherence