How do you convert units within a measurement system

You have to know how the value of one unit corresponds to the value of the other unit. For example you have to know that there are 100 cm in 1 m or 1000 m in 1 km. It's easy in metric measurement system because it's all about multiplying/dividing by 10 or its multiplications. But in American/English system you just have to learn the values.

For example:

1 km = 1000 m = 10000 dm = 100000 cm = 1000000 mm

But:

1 mile = 1760 yards = 5280 feet = 63360 inches