For converting between two systems you need to know relations. For example 1 yard is 0.9144 meters. So every other number of yd you need to multiply by above number to get meter.
There are units for many different things. But basically, you look up the conversion factor, then multiply or divide. It is safest (so as not to multiply when you should divide, or vice versa) to...
All metric units of a particular type, ie lengths, areas, volumes, weights, etc are convertible with scales of 10, 100, 1000, and so on. The size of the unit in question is determined by a prefix,...
Well, the only time you'd use this is in displacement of an irregular solid to find its density. In that case, if a liquid got displaced 200ml, you can convert it to cm3 like this: 200ml=200cm3