Well the way it was always explained to me was by drawing a little chart like this:

km hm dam m dm cm mm

You’d start with cm and move over to km which would be 5 spaces. Then you’d move the decimal place to the left 5 places since you’re going to the left on the chart. And vice versa, if you’re going to right on the chart, you’d move the decimal point to the right.

km – kilometer

hm – hectometer

dam – dekameter

m – meter

dm – decimeter

cm – centimeter

mm – millimeter

It works the same for liters and grams as well. Just substitute out meter. I hope this helps. The metric system is very easy to understand once you know what you’re doing. I don’t know why the US doesn’t use it.

cm to km is 5 steps higher

meaning a lower number

move the decimal left