Why are milliter and cubic centimeters the same?

Answer 1

Every unit in the International Standards of Units ("SI units") has a universal standardized definition. By universal, it is used everywhere. For instance, a meter is defined as "Length of the path travelled by light in a vacuum in 1⁄299,792,458 of a second (17th CGPM)" Yes. The definitions are usually pretty weird, but they stay consistent, which is important.

Now, the reason why the milliliter and the cubic centimeter are the same is much simpler. The liter was originally created as another word for a cubic decimeter. Because there are 1000 milliliters in a liter, and 1000 cubic decimeters in a cubic centimeter[see note], a milliliter and a cubic centimeter and therefore, the same.

Note: millimeter, centimeter, decimeter. While the centimeter is 10 times smaller than the decimeter, we are also dealing with cubic terms, so a cubic centimeter is therefore, 103 or 1000 times smaller than a cubic decimeter.