How many square kilometers is the earth?

Answer 1

"Okeanos (Oceanus) in Greek) is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (an area of some 361 million square kilometers) is covered by ocean"

- Ocean; Wikipedia

By this estimate, Earth is approximately 508.45 million square kilometers.

.71x = 361

x = 508.45
510,072,000 km squared, total. About 30 percent land About 70 percent water See link for more information.