What is a centimeter?
A centimeter (cm) is one hundredth of a meter and just under four tenths of an inch (0.3937 inches). The prefix comes from the Latin centum, a hundred.
Divide centimeters by 30.48 to get feet, or multiply feet by 30.48 to get centimeters. The factor is exact, as a foot is 30.48cm, and a single centimeter is about 0.0328 feet.
The centimeter was the base unit of length in the CGS (centimeter, gram, second) system that physicists used before SI, which is why older physics talks about dynes and ergs.
What is a kilometer?
A kilometer is 1,000 meters, or about 0.621 miles. 'Kilo' is the Greek-derived prefix for a thousand. It is the unit for road distances nearly everywhere except the US and UK, which still use miles.
A kilometer is about 3,281 feet or 39,370 inches. At a walking pace of 5km/h it takes about 12 minutes to cover.
Going from kilometers to meters just means moving the decimal point three places. A mile has to be broken into 1,760 yards or 5,280 feet first, and neither of those is a round number of anything.