Centimeters to kilometers (cm to km)

One centimeter is exactly 0.00001 kilometers, or 10^-5. Both are the meter with a prefix attached, so this is a shift of the decimal point by five places and not a conversion between two different systems at all.

Worked through: 50,000 cm x 0.00001 = 0.5 km.

Going the other way, one kilometer is 100,000 centimeters.

For mental arithmetic: Move the decimal point five places left. 250,000 cm is 2.5 km.

Five orders of magnitude apart, which is the real difficulty: the answer almost always has leading zeros and that is where errors creep in. 100,000 centimeters is exactly 1 kilometer. That is the anchor worth memorizing, and everything else scales from it. The conversion turns up in map scales and in CAD drawings, where a model dimensioned in centimeters has to be placed on a plan dimensioned in kilometers.

Precision is worth matching to the input. A measurement given as 100 cm carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.