Hello Games lead and No Man's Sky creator Sean Murray once was on record to say that planets in No Man's Sky were just as big as Earth. Not that we need anymore proof that some things were fabricated in the marketing of the game, but yeah, that wasn't correct either. While the planets are big, they are no where near the size of Earth even in scale. TheyCallMeConor walked halfway across a random planet and it took him 12 hours to do. If you were to walk halfway across the Earth...you would walk roughly 12,000 miles. Even if you're a really fast speed walker you're gonna come up short. 

You can see his efforts in the video below. Don't worry they speed it up. Thanks VG247 for giving us the heads up. By the way we're on about 2 weeks of silence from Murray since the PC version completely crapped out.