Are you American? As a European, I did not even think twice about this. Kilometers (km) is how we measure distance. 1000 km = 1k km, not 1Mm (nobody ever uses

Are you American? As a European, I did not even think twice about this. Kilometers (km) is how we measure distance. 1000 km = 1k km, not 1Mm (nobody ever uses that), so it follows that 50000 km = 50k km.