Km is 103m cm is 10-2m so the difference is 105 i.e. 100000 (one with 5 zeroes)
Or more intuitively one centi-meter is a 1/100 of a meter and Kilo-Meter is 1000 meter therefore 100*1000 100000
It is quite intuitive, once you start using it
What’s weird is why we don’t use Megameters and megagrams (i.e. one metric ton)
Alleluja, you have seen the light