Since a kilometer is just 1000m, just divide that number by 1000 (that is to say, move the decimal three places to the left).
2420453 m = 2420.453 km
0.675 kilometers.
That would be 41 kilometers
13 km = 13,000 m
0.001km
250 meters = .25 kilometers
120 m = 0.12 km
25.43 km
100 m
5km
2300 m
2.4 kilometers.
5000 m