It's not an approximation... To convert from m/s to km/h you need to divide by 1000 (there are 1000 meters in 1 km) and multiply by 3600 (there are 3600 second

It's not an approximation... To convert from m/s to km/h you need to divide by 1000 (there are 1000 meters in 1 km) and multiply by 3600 (there are 3600 seconds in 1 hour). So 3600/1000 = 3.6